ATSAMDA1G14B - Electronic component Microchip - Free user manual and instructions

USER MANUAL ATSAMDA1G14B Microchip

QTouch Library Peripheral Touch Controller

USER GUIDE

Description

Atmel ^® QTouch ^® Peripheral Touch Controller (PTC) offers built-in hardware for capacitive touch measurement on sensors that function as buttons, sliders, and wheels. The PTC supports both mutual and self-capacitance measurement without the need for any external component. It offers superb sensitivity and noise tolerance, as well as self-calibration, and minimizes the sensitivity tuning effort by the user.

The PTC is intended for autonomously performing capacitive touch sensor measurements. The external capacitive touch sensor is typically formed on a PCB, and the sensor electrodes are connected to the analog charge integrator of the PTC using the device I/O pins. The PTC supports mutual capacitance sensors organized as capacitive touch matrices in different X-Y configurations, including Indium Tin Oxide (ITO) sensor grids. In mutual capacitance mode, the PTC requires one pin per X-line (drive line) and one pin per Y-line (sense line). In self-capacitance mode, the PTC requires only one pin with a Y-line driver for each self-capacitance sensor.

Features

• Implements low-power, high-sensitivity, environmentally robust capacitive touch buttons, sliders, and wheels
  • Supports mutual capacitance and self-capacitance sensing
• Up to 32 buttons in self-capacitance mode
• Up to 256 buttons in mutual capacitance mode
  • Supports lumped mode configuration
  • One pin per electrode - no external components
• Load compensating charge sensing
  • Parasitic capacitance compensation for mutual capacitance mode
• Adjustable gain for superior sensitivity
  • Zero drift over the temperature and VDD range
  • No need for temperature or VDD compensation
• Hardware noise filtering and noise signal de-synchronization for high conducted immunity
• Atmel provided QTouch Library firmware and QTouch Composer tool

Product Support

For assistance related to QTouch capacitive touch sensing software libraries and related issues, contact your local Atmel sales representative or log on to myAtmel Design Support portal to submit a support request or access a comprehensive knowledge base.

If you do not have a myAtmel account, please visit http://www.atmel.com/design-support/ to create a new account by clicking on Create Account in the myAtmel menu at the top of the page.

When logged in, you will be able to access the knowledge base, submit new support cases from the myAtmel page or review status of your ongoing cases.

Table of Contents

Description....1

Features....1

1. Development Tools .... 5

2. Device Variants Supported....6

3. Capacitive Touch Technology....8

3.1. Capacitive Touch Sensors....8
3.2. Capacitance Measurement Methods....8
3.3. Self-capacitance Measurement Method....8
3.4. Mutual Capacitance Measurement Method....9
3.5. Capacitive Touch Lumped Sensors....9
3.6. Capacitive Touch Low Power Sensor....11
3.7. PTC and its Benefits....13
3.8. PTC Block Diagram for Self-capacitance and Mutual Capacitance Method.... 13
3.9. Design Approach with PTC....15
3.10. Capacitive Touch Development Cycle....16

4. Touch Sensor Debug and Status Information.... 17

4.1. Signal....17
4.2. Reference....17
4.3. Delta....18
4.4. Touch Status & Slider/Wheel Position....19

5. QTouch Library....20

5.1. Overview....20
5.2. Library Parameters....21
5.3. Moisture Tolerance 42
5.4. Reading Sensor States....44
5.5. Application Flow....44
5.6. API Sequence....46
5.7. State Machine....47
5.8. Operation Modes....50
5.9. Touch Library API Error....52

6. Tuning for Noise Performance....54

6.1. Noise Sources....54
6.2. Noise Counter Measures....54

7. Application Design....60

7.1. Touch Library and Associated Files....60
7.2. Code and Data Memory Considerations....60

8. Example Applications.... 63

8.1. Atmel Board Example Projects....63
8.2. User Board Example Projects....66
8.3. Using Atmel Software Framework (ASF) with the Example Projects.... 67
8.4. Using Xplained Pro Kit to Program User Board.... 67
8.5. Using QDebug Touch Data Debug Communication Interface.... 67
8.6. Using Xplained Pro Kit for QDebug Data Streaming from User Board.... 68
8.7. Using Atmel ICE for QDebug Data Streaming from User Board.... 70

9. Known Issues....71

10. FAQ on PTC Qtouch....73

11. Appendix....74

11.1. Macros....74
11.2. Typedef....76
11.3. Enumeration....76
11.4. Datastructures....84
11.5. Global Variables....92
11.6. API....93

12. Revision History....100

1. Development Tools

The following development tools are required for developing QTouch library using PTC:

- Development Environment for GCC Compiler:

– QTouch Composer 5.9.116 or later versions

– QTouch Library 5.9.211 or later versions

Note: The QTouch Library and Composer extensions work only with Atmel Studio 7 which can be downloaded from http://www.atmel.com/

– Dependent Atmel Studio Extensions

• Atmel Software Framework 3.30.1 or later versions
• Atmel Kit Extension 7.0.70 or later versions

• Development Environment for IAR Compiler:

- IAR Embedded Workbench ^ for ARM ^ 7.50.1.10273 or later

- IAR Embedded Workbench for Atmel AVR ^ 6.70.1 or later

- Atmel Software Framework 3.29.0 or later (optional)

- Atmel QTouch Library 5.9.211 IAR Installer (available at http://www.atmel.com/tools/qtouchlibraryptc.aspx)

2. Device Variants Supported

QTouch Library for SAM and ATmega devices are available for the following device variants:

Series Variant
SAM D20 J Series ATSAMD20J18, ATSAMD20J17, ATSAMD20J16, ATSAMD20J15, ATSAMD20J14
SAM D20 G Series ATSAMD20G18, ATSAMD20G18U, ATSAMD20G17, ATSAMD20G17U, ATSAMD20G16, ATSAMD20G15, ATSAMD20G14
SAM D20 E Series ATSAMD20E18, ATSAMD20E17, ATSAMD20E16, ATSAMD20E15, ATSAMD20E14
SAM D21 J Series ATSAMD21J18A, ATSAMD21J17A, ATSAMD21J16A, ATSAMD21J15A, ATSAMD21J16B, ATSAMD21J15B
SAM D21 G Series ATSAMD21G18A, ATSAMD21G17A, ATSAMD21G16A, ATSAMD21G15A, ATSAMD21G15B, ATSAMD21G16B, ATSAMD21G17AU, ATSAMD21G18AU
SAM D21 E Series ATSAMD21E18A, ATSAMD21E17A, ATSAMD21E16A, ATSAMD21E15A, ATSAMD21E15B, ATSAMD21E15BU, ATSAMD21E16B, ATSAMD21E16BU
SAM D10 C Series ATSAMD10C14A
SAM D10 D Series ATSAMD10D14AM, ATSAMD10D14AS, ATSAMD10D14AU
SAM D11 C Series ATSAMD11C14A
SAM D11 D Series ATSAMD11D14AM, ATSAMD11D14AS, ATSAMD11D14AU
SAM L21 E Series ATSAML21E15B, ATSAML21E16B, ATSAML21E17B, ATSAML21E18B
SAM L21 G Series ATSAML21G16B, ATSAML21G17B, ATSAML21G18B
SAM L21 J Series ATSAML21J16B, ATSAML21J17B, ATSAML21J18B
SAM R21 E Series ATSAMR21E16A, ATSAMR21E17A, ATSAMR21E18A, ATSAMR21E19A
SAM R21 G Series ATSAMR21G16A, ATSAMR21G17A, ATSAMR21G18A
SAM DA1 E Series ATSAMDA1E14A, ATSAMDA1E15A, ATSAMDA1E16A
SAM DA1 G Series ATSAMDA1G14A, ATSAMDA1G15A, ATSAMDA1G16A
SAM DA1 J Series ATSAMDA1J14A, ATSAMDA1J15A, ATSAMDA1J16A
SAM C21 E Series ATSAMC21E15A, ATSAMC21E16A, ATSAMC21E17A, ATSAMC21E18A
SAM C21 G Series ATSAMC21G15A, ATSAMC21G16A. ATSAMC21G17A, ATSAMC21G18A
SAM C21 J Series ATSAMC21J16A, ATSAMC21J17A, ATSAMC21J18A
SAM C20 E Series ATSAMC20E15A, ATSAMC20E16A, ATSAMC20E17A, ATSAMC20E18A
SAM C20 G Series ATSAMC20G15A, ATSAMC20G16A. ATSAMC20G17A, ATSAMC20G18A
SAM C20 J Series ATSAMC20J16A, ATSAMC20J17A, ATSAMC20J18A
SAM L22 G Series ATSAML22G16A, ATSAML22G17A, ATSAML22G18A
SAM L22 J Series ATSAML22J16A, ATSAML22J17A, ATSAML22J18A

SeriesVariant

SAM L22 N Series ATSAML22N16A, ATSAML22N17A, ATSAML22N18A

ATmega Series ATmega328PB, ATmega324PB

3. Capacitive Touch Technology

3.1. Capacitive Touch Sensors

Capacitive touch sensors replace conventional mechanical interfaces and operate with no mechanical wear and are closed to the environment. They provide greater flexibility in industrial design and result in differentiating end product design. For more information, refer Capacitive Touch Lumped Sensors and Capacitive Touch Low Power Sensor.

Figure 3-1. Sensor Types

Sensor Types Buttons Sliders Wheels Buttons Slider Wheel

3.2. Capacitance Measurement Methods

Self-capacitance measurement method involves charging a sense electrode of unknown capacitance to a known potential. The resulting charge is transferred into a measurement circuit. By measuring the charge with one or more charge-and transfer cycles, the capacitance of the sense plate can be determined.

Figure 3-2. Capacitance Measurement Principle

graph TD
    A["Charge Transfer"] --> B["Self-Capacitance"]
    A --> C["Mutual-Capacitance"]
    D["Measurement Method"] --> E["Input: Left"]
    D --> F["Output: Right"]

Mutual capacitance measurement method uses a pair of sensing electrodes. One electrode acts as an emitter into which a charge consisting of logic pulses is driven in burst mode. The other electrode acts as a receiver that couples to the emitter using the overlying panel dielectric. When a finger touches the panel, the field coupling is reduced, and touch is detected.

3.3. Self-capacitance Measurement Method

• Uses a single sense electrode (Y-line)
- Self-capacitance button can be formed using one channel
- Self-capacitance slider and wheel is formed using 3 channels
- Robust and easy to use, ideal for low sensors count

Figure 3-3. Self-capacitance Method

graph LR
    A["Atmel MCU with PTC"] -->|Y0| B["Sensor 0"]
    A -->|Y1| B
    A -->|Y2| B
    A -->|Y3| B
    B --> C["Sensor 1"]

3.4. Mutual Capacitance Measurement Method

• Uses a pair of sense electrodes (X-Y lines)
- Mutual capacitance buttons use one X-Y channel
- Mutual capacitance sliders and wheels can be configured to use 3 to 8 X-Y channels, depending on the sensor size
• Suitable for high sensor count
• Better moisture tolerance

Figure 3-4. Mutual Capacitance Method

graph TD
    A["Atmel MCU with PTC"] --> B["X0"]
    A --> C["X1"]
    A --> D["X2"]
    A --> E["Y0"]
    A --> F["Y1"]
    A --> G["Y2"]
    B --> H["Output Dot 1"]
    C --> I["Output Dot 2"]
    D --> J["Output Dot 3"]
    E --> K["Output Dot 4"]

3.5. Capacitive Touch Lumped Sensors

Lumped sensor configuration is a combination of multiple sense lines (Self-capacitance measurement) or multiple drive and sense lines (Mutual capacitance measurement) to act as one single sensor. Lumped mode acts as a tool for application developers to improve overall system performance.

Improved Power Efficiency

When multiple sensors are lumped together and treated as one single sensor the time taken to perform scans is reduced. For battery powered applications using multiple buttons, a group of touch sensors can be lumped to form a single lumped sensor and this sensor alone can be scanned, thereby resulting in reduced power consumption. Upon user presence detection on the lumped sensor all configured sensors in the system can then be scanned individually.

Improved Response Time

In high key-count applications, there can be a significant latency between touching a sensor and the detection of a touch contact. This is due to the time taken to sequentially measure the capacitance of each key on each measurement cycle. With a Lumped mode implementation this latency can be reduced by arranging the sensors into groups. When one of those lumped groups shows touch detection, only the keys within that group are individually measured to determine which is touched.

E.g. A keyboard consisting 64 keys may be divided into 8 lumped groups of 8.

Thus, each measurement cycle is reduced to measure only the 8 lumped sensors. When a touch contact is applied, first the lump sensor shows touch delta, then the 8 component keys are scanned and the location is resolved. Only 16 measurements are required to resolve the touch status of all keys, compared to 64 measurements in the traditional sequential scan of all keys.

It offers an additional edge during low power acquisition as a group of keys [in lumped configuration] can be scanned thus reducing the power consumed drastically. Each sensor has its own pre-scaled clock and series resistor for improved noise immunity.

Figure 3-5. Self-capacitance Sensors connected to PTC

graph LR
    A["Atmel"] -->|Y0| B["Sensor 1"]
    C["MCU"] -->|Y1| D["Sensor 2"]
    C -->|Y2| E["Sensor 3"]
    C -->|Y3| F["Sensor 4"]
    A --> G["With PTC"]

Figure 3-6. Lumped Self-capacitance Sensors connected to PTC

graph LR
    A["Atmel"] -->|Y0| B["Lumped Sensor"]
    C["MCU"] -->|Y1| B
    D["With PTC"] -->|Y2| B
    D -->|Y3| B

In the preceding figures, individual buttons are shown along with the lumped equivalent for self-capacitance arrangement.

Lumped Mode Pin and Sensor Configuration for Self-capacitance Method:

#define DEF_SELFCAP_LINES Y(5), Y(4), Y(11), Y(10), Y(13), Y(7), Y(12), Y(6), LUMP_Y(5,4)
touch_ret = touch_selfcap_sensor_config(SENSOR_TYPE_LUMP, CHANNEL_8, CHANNEL_8, NO_AKS_GROUP, 40u, HYST_6_25, RES_8_BIT, &sensor_id); 

Figure 3-7. Lumped Sense Lines Mutual Capacitance Sensors connected to PTC

graph TD
    A["Atmel"] -->|X0| B["Lumped Sensor"]
    C["MCU"] -->|X1| B
    D["With PTC"] -->|Y0| B

In the preceding figure, mutual capacitance lumped sensor configuration is presented.

Lumped Mode Pin and Sensor Configuration for Mutual Capacitance Method:

#define DEF_MUTLCAP_NODES X(8), Y(10), X(9), Y(10), X(2), Y(12), X(3), Y(12), \X(8), Y(12), X(9), Y(12), X(2), Y(13), X(3), Y(13), \X(8), Y(13), X(9), Y(13), LUMP_X(2,3,8,9), LUMP_Y(10,13)

touch_ret = touch_mutlcapp_sensor_config(SENSOR_TYPE_LUMP, CHANNEL_10, CHANNEL_10, NO_AKS_GROUP, 20u, HYST_6_25, RES_8_BIT, 0, &sensor_id); 

Limitations of Use

Lumped sensor capacitive load should not exceed the maximum sensor load for individual sensors in either mutual or self-capacitance modes. Lumped mode treats the larger sensors as one single sensor therefore the maximum lumped sensor load should also observe this specification, else this will result in calibration error.

In mutual capacitance measurement mode the capacitive load of each sensor is normally much lower than that of the self-capacitance method. It is therefore possible as a general rule to use more mutual sensors together as a single lumped sensor.

The user can ensure that the lumped sensor does not result in a calibration error (value of 0x80) using p_xxxxcap_measure_data->p_sensors[].state variable.

3.6. Capacitive Touch Low Power Sensor

The QTouch Library may be configured to operate PTC touch sensing autonomously using the Event System. In this mode, a single sensor is designated as the 'Low Power' key and may be periodically measured for touch detection without any CPU action. The CPU may be held in deep sleep mode throughout the operation, minimizing power consumption.

The low power key may be a discrete electrode with one Y (Sense) line for Self-capacitance or One X (Drive) plus one Y (Sense) for mutual capacitance, or it may be a combination of multiple Drive and/or Sense lines as a Lumped mode sensor.

Figure 3-8. Low Power Flow

graph TD
    A["touch_xxxx_sensors_init()"] --> B["touch_xxxx_sensors_config()"]
    B --> C["touch_xxxx_sensors_calibrate()"]
    C --> D["touch_xxxx_sensors_measure (NORMAL_ACQ_MODE)"]
    D --> E["Host Application Code /SLEEP"]
    E --> F{Is Calibration Completed?}
    F -->|No| E
    F -->|Yes| G["touch_xxxx_sensors_measure (NORMAL_ACQ_MODE)"]
    G --> H{Is touch_inactivity_time >= NO_ACTIVITY triggers_TIME}
    H -->|No| G
    H -->|Yes| I["touch_xxxx_lowpower_sensor_enable_event_measure()"]
    I --> J["Host Application Code /SLEEP"]
    J --> K["End"]

    subgraph 'Calibration starts when first time call to measure sensors API after sensors calibrate API.'
        L["PTC ISR (Sensors Calibration)"] --> D
        L --> M["measurement_complete_callback(), measured data and Touch Status"]
        L --> N["filter_callback(), if enabled"]
        L --> O["measurement_complete_callback(), measured data and Touch Status"]
        P["PTC ISR"] --> Q["WAKE_UP_TOUCH=1"]
    end

Active Measurement Mode

In the active measurement mode all configured sensors are measured at DEF TOUCH MEASUREMENT PERIOD MS millisecond scan interval.

The user application arrangement could be designed such that when no touch activity is detected on any of the configured sensors for NO_ACTIVITY_TRIGGER_TIME milliseconds, then the application switches to low power measurement mode.

Low Power Measurement Mode

In the low power measurement mode, a designated sensor or a lumped sensor can be scanned as a single sensor. In this mode, the system is in standby sleep mode, the CPU and other peripherals are in sleep, excepting for the event system, the RTC and the PTC module / WDT and PTC module in SAM / Mega devices. A user touch on the designated low power sensor will cause the CPU to wake up and perform active measurement in order to resolve the touch. To keep reference tracking of the designated low power sensor, the RTC/WDT is configured to periodically wake up the CPU every DEF_LOWPOWER_SENSOR_DRIFT_PERIODICITY_MS millisecond to perform one active measurement.

Switching between Active Mode and Low Power Mode

When switching from active to low power mode, all sensors except the lumped sensor are disabled. So, no reference tracking is performed on these sensors during the low power mode. When a touch is detected on the lumped sensor, all disabled sensors shall now be re-enabled and measurement is initiated on the sensors. If the device is in sleep for a very long time, then it is recommended to force calibration on the re-enabled sensors to ensure proper reference values on these sensors.

3.7. PTC and its Benefits

• Mixed Hardware + Firmware solution, allows user to define sensor configuration
• Peripheral Touch Controller + QTouch library
  PTC runs data acquisition autonomously, resulting in low CPU utilization and power consumption
• User controlled power-performance trade-off
  – CPU can sleep during acquisition to save power
• Alternatively, CPU can perform other time critical operations during touch acquisition
• Robust noise performance

Figure 3-9. User Application with PTC Device

Atmel MCU User Application QTouch Library PTC

3.8. PTC Block Diagram for Self-capacitance and Mutual Capacitance Method

The PTC block diagram for self-capacitance measurement is shown in the following figure. Only Y-lines can be connected to self-capacitance sensors and are selected using the Input control. X-lines remain unused and can be used for any other GPIO functionality. The acquisition module along with the compensation circuit helps in measuring the change in capacitance due to user touch.

Figure 3-10. PTC Self-capacitance Method - Block Diagram

graph LR
    A["Cy0"] --> B["Input control"]
    C["Cy15"] --> D["Input control"]
    B --> E["Compensation Circuit"]
    D --> E
    E --> F["Acquisition Module\n• Gain control\n• ADC\n• Filtering"]
    F --> G["Result 10"]
    F --> H["X Line Driver"]
    I["Y0"] --> J["Block"]
    K["Y1"] --> J
    L["Y15"] --> J
    J --> M["Rs 100K"]
    M --> F
    N["IRQ"] --> F

The PTC block diagram for mutual capacitance measurement is as shown in the following figure. Both X-lines and Y-lines should be connected to mutual capacitance sensors and are selected using the Input control.

Figure 3-11. PTC Mutual Capacitance Method - Block Diagram

graph TD
    A["Input control"] --> B["Compensation Circuit"]
    B --> C["Acquisition Module"]
    C --> D["X Line Driver"]
    D --> E["Feedback Loop"]
    E --> F["Output"]
    subgraph Input
        G1["+"]
        G2["-"]
        G3["-"]
        G4["-"]
        G5["-"]
        G6["-"]
        G7["-"]
        G8["-"]
        G9["-"]
    end
    subgraph Control
        H0["Y0"]
        H1["Y1"]
        H2["Y15"]
        H3["X0"]
        H4["X1"]
        H5["X15"]
    end
    subgraph Feedback
        I["Rs"]
        J["100K"]
    end
    K["IRQ"] --> L["Result"]
    M["10"] --> N["Feedback Loop"]

3.8.1. Compensation Circuit

The PTC has an internal compensation circuit which is used to compensate the sensor capacitance. Both self-capacitance and mutual capacitance sensing modes have the same compensation range. But the mutual capacitance mode can compensate more parasitic capacitance compared to self-capacitance mode.

The tag_touch_measure_data_t structure contains the p_cc_calibration_vals parameter which represents the current channel's compensation circuit value. For more information, refer Measure Data Type (tag_touch_measure_data_t).

Compensation circuit value used in pF = (p_cc_calibration_vals[channel_no] & 0x0F) * 0.00675 + ((p_cc_calibration_vals[channel_no] >> 4) & 0x0F) * 0.0675 + ((p_cc_calibration_vals(channel_no] >> 8) & 0x0F) * 0.675 + ((p_cc_calibration_vals(channel_no] >> I2) & 0x3) * 6.75 

Also, the touch_xxxxcap_sensors_calibrate function helps the user to calibrate the compensation circuit according to the sensors used. If the routine fails to calibrate the compensation circuit due to saturation, the measurement will return TOUCH_CC_CALIB_ERROR. The compensation circuit could have

exceeded its limit. The specific sensor that has failed can be determined using

p_xxxxcap_measure_data->p_sensors[].statewhen it contains the value of SENSOR_CALIBRATION_ERROR(0x80u).

• Typical compensation circuit value for the self-capacitance mode ranges from 10 to 25 pF and for the mutual capacitance mode it is around 2 pF.
• The compensation circuit value is affected by sensor size and the ground surrounding the sensor or trace. The compensation circuit value ranges from 0.00675 pF to 31.48 pF.
• If the compensation circuit value exceeds the limit, to reduce the value, use a mesh instead of a solid plane in the sensor and ground plane.
  • For detailed sensor design, refer http://www.atmel.com/images/doc10752.pdf.

3.9. Design Approach with PTC

Two design approaches are possible when using Atmel MCU along with PTC. The Atmel MCU could be predominantly used as an MCU for touch measurement. Else, the Atmel MCU can function as a Host MCU utilizing peripherals such as the USB, ADC, DAC, SERCOM, DMA and GPIO along with the PTC used for "on-chip" touch functionality.

The design approaches are:

• Atmel MCU with PTC predominantly functioning as a touch MCU
  – Used for touch sensor status and rotor/slider position detection
• Additionally used to indicate touch status using LED, buzzer etc
  – Sends touch status and rotor/slider position information to a Host MCU
• Atmel MCU functions as a Host MCU with on-chip touch functionality
• Can be a cost saving design as a single chip solution with on-chip touch functionality
• Utilizes other on-chip peripheral for a desired user application

Figure 3-12. PTC Design Approach

graph LR
    A["Host MCU"] -->|I2C, SPI, UART, GPIO or user defined interface| B["User Application"]
    B --> C["QTouch Library + PTC"]
    C --> D["Sensors"]
    D --> E["Wheel"]
    D --> F["Slider"]
    D --> G["Keys"]
    D --> H["Buttons, Sliders, Wheels"]
    style A fill:#ccc,stroke:#333
    style B fill:#ff9999,stroke:#333
    style C fill:#ffcc99,stroke:#333
    style D fill:#ffcccc,stroke:#333
    style E fill:#ffffff,stroke:#333
    style F fill:#ffffff,stroke:#333
    style G fill:#ffffff,stroke:#333
    style H fill:#ffffff,stroke:#333

Touch Status Indicator
LED PWM, GPIO Pin toggle, Buzzer

3.10. Capacitive Touch Development Cycle

The capacitive touch development cycle involves PCB board design to develop the user interface hardware as well as firmware application development. The QTouch Composer PC software available as part of Atmel Studio extension gallery allows for PTC QTouch Library projects to be generated automatically with a desired user configuration for touch sensors. The QTouch Composer also allows for touch sensor data analysis and performance tuning for sensitivity and noise.

Figure 3-13. Capacitive Touch Development Cycle

graph TD
    A["Device variant & Touch technology selection"] --> B["Sensor design, PCB board design"]
    B --> C["Application development"]
    C --> D["Performance tuning"]
    D --> E["QTouch Prototype"]
    F["QTouch Composer"] --> G["PTC Acquisition method selection"]
    F --> H["Code, Data memory requirements, PTC Pin selection"]
    F --> I["Touch Sensor data & waveform analysis"]
    F --> J["Touch Response time"]
    F --> K["PTC Device selection"]
    F --> L["Example project Creation, ASF services"]
    F --> M["QTouch Library parameter tuning"]
    F --> N["Touch Sensitivity & Noise performance tuning"]
    O["QTouch Analyzer"] --> F
    P["QTouch Project Builder"] --> F
    Q["QTouch Example Application"] --> F

4. Touch Sensor Debug and Status Information

The touch sensor debug information necessary for tuning of the sensors are signal, reference, delta, and compensation capacitance. While the signal, reference and delta help in sensitivity and noise tuning the sensor parameters, the compensation capacitance is an indicator for extreme sensor design. The sensor status and position information are parameters that must be judged by the user application to initiate the relevant touch action.

4.1. Signal

Signal value is the raw measurement data on a given touch channel. The value increases upon touch.

Figure 4-1. Channel Signal

QTouch Analyzer - AtmierStudio (Administrator) File Edit View V Assist X ASF Project Debug Tools Window Help SAM D21 Xplained Pro - 6444 Start Page QTouch Start Page QTouch Analyzer QDEBUG_DGI - 06444 ReConnect Start Reading Save Trace Open Trace File Save Design File Save Csw File No Solution Found Help Virtual Kit View Signal Selection Automatic Scale Manual Scale Snapshot Default Camera View Sensor Specific Global Button0 Signal Delta Reference Detect Threshold Detect Hysteresis In Detect Events Kit/Sensor Properties Button 0 < Button0> Untouched Touched Untouched Physical Hardware AKS Group NO_AK Detect Threshold 30 Detect Hysteresis HYST_E Positive Recalibration Flag False From Channel 0 To Channel 0 Write up to Caps from Kit Write To Project samples Min: 1 Max: 1050 Play 14:29:11.278 14:29:11.978 14:29:12.674 14:29:13.375 14:29:14.070 14:29:14.570 14:29:15.078 14:29:15.554 14:29:16.146 14:29:16.549 14:29:17.176 14:29:17.650 34 Connected New List Entire Solution O Errors Warnings B Messages Build + IntelliSense Search Error List Ready

4.2. Reference

Reference value of a touch channel is the long term average measurement on a specific channel.

It represents:

• Resting signal when there is no touch
• Initial value obtained during the calibration process
  • Reference is adapted by Drift Compensation algorithm

Figure 4-2. Channel Reference

QTouch Analyzer - AtmelStudio (Administrator) File Edit View Assist ASF Project Debug Tools Window Help Debug Remaster No Device No Seed SAM 021 Xplamed Pro - 6444 Start Page QTouch Start Page QTouch Analyzer QDBBLXI_DGI - 36444 BeConnect Start Reading Save Trace Open Trace File Save Design File Save Cox File No Solution Found Help Virtual Kit View Graph View Tabular View Signal Selection Automatic Scale Manual Scale Snapshot Default Camera View Kit/Sensor Properties Button D - (ButtonD) + Sensor Specific Global Button0 Signal Delta Reference Detect Threshold Detect Hyderness In Detect Events AKS Group NO_AE Detect Threshold 30 Detect Hyderness H51.1 Positive Recalibration Flag False From Channel 0 To Channel 0 Min: 1 Max: 1050 Play: 243747.688 14:37:47.906 14:37:47.912 14:37:47.956 14:37:48.001 14:37:48.047 14:37:48.091 14:37:48.137 14:37:48.182 14:37:48.226 14:37:48.271 14:37:48.271 Connected Error List Entire Solution 0 Errors 0 Warnings 0 Messages Build - IntelliSense Search Entry List Ready

4.3. Delta

Delta value of a touch channel represents touch strength.

• Delta = (signal - reference)
  • Deltas increase with touch

Figure 4-3. Sensor Delta

QTouch Analyzer - AtmelStudio (Administrator) File Edit View VAutoX ASF Project Debug Tools Window Help Debug Presser SAM D21 Xplained Pro - 6444 Start Page QTouch Start Page QTouch Analyzer QDEBUG_DQ - 06444 ReConnect Start Reading Save Trace Open Trace File Save Design File Save Cov File No Solution Found Help Virtual Kit View Graph View Tabular View Signal Selection Automatic Scale Manual Scale Snapshot Default Camera View Sensor Specific Global button0 Signal Delta Reference Detect Threshold Detect Hyderness In Detect Events AKS Group NO_AK Detect Threshold 30 Detect Hysteresis HVST Positive Recalibration Rag False From Channel 0 To Channel 0 Name to kit Copy Text Set Delete To Project samples Min: 0 Max: 880 Play 1452:19.683 1452:20.783 1452:21.208 1452:21.634 1452:22.065 1452:22.490 1452:22.935 1452:23.255 1452:23.680 1452:24.070 1452:24.290 1452:24.714 1452:2 Connected Error list Entire Solution 0 Errors 0 Warnings 0 Messages Build + IntelliSense Search Error List Ready

4.4. Touch Status & Slider/Wheel Position

The sensor touch status is the primary touch sensor information utilized by a user application. The sensor state can either be ON or OFF. For sliders and wheel, additionally the touch position is of interest. For an 8-bit resolution, the touch position ranges from 0 to 255 end-to-end. It is possible to configure with a lower resolution by configuring setting in the touch library. The sensor touch status and slider/wheel position must always be used once the library completes the measurements.

The touch sensor state for mutual capacitance or self-capacitance sensor can be obtained by reading the following boolean variables.

bool sensor_state_self = GET_SELFCAP_SENSOR_STATE(SENSOR_NUMBER);
bool sensor_state_mut1 = GET_MUTLCAP_SENSOR_STATE(SENSOR_NUMBER); 

The touch sensor rotor or slider position information for mutual capacitance or self-capacitance sensor can be obtained using the following parameters.

uint8_t rotor_slider_position_self = GET_SELFCAP_ROTOR_SLIDER_POSITION(ROTOR_SLIDER_NUMBER);
uint8_t rotor_slider_position_mut1 = GET_MUTLCAP_ROTOR_SLIDER_POSITION(ROTOR_SLIDER_NUMBER); 

The touch sensor noise status for mutual capacitance or self-capacitance sensor can be obtained using the following parameters.

bool sensor_noise_state_self = GET_SELFCAP_SENSOR_NOISE_STATUS(SENSOR_NUMBER);
bool sensor_noise_state_mut1 = GET_MUTLCAP_SENSOR_NOISE_STATUS(SENSOR_NUMBER); 

5. QTouch Library

Atmel QTouch Library makes it simple for developers to embed capacitive touch button, slider, wheel functionality into general purpose Atmel SMART | ARM and AVR ^® microcontroller applications. The royalty-free QTouch Library provides several library files for each device and supports different numbers of touch channels, enabling both flexibility and efficiency in touch applications.

QTouch Library can be used to develop single-chip solutions for many control applications, or to reduce chip count in more complex applications. Developers have the latitude to implement buttons, sliders, and wheels in a variety of combinations on a single interface.

Figure 5-1. QTouch Library

graph TD
    A["Custom Code"] --> B["Compiler"]
    B --> C["Link"]
    C --> D["Application"]
    B --> E["Atmel Qtouch Library"]

5.1. Overview

QTouch Library API for PTC can be used for touch sensor pin configuration, acquisition parameter setting as well as periodic sensor data capture and status update operations. The QTouch Library in turn interfaces with the PTC module to perform the necessary action. The PTC module interfaces with the external capacitive touch sensors and is capable of performing self and mutual capacitance method measurements. The library features low power and lumped mode configuration.

Figure 5-2. QTouch Library Overview

graph TD
    A["Host Application"] --> B["Qtouch Library API"]
    B --> C["Sensor Channel/ Pin Configuration"]
    B --> D["Sensor Parameter Setting"]
    B --> E["Sensor Status / Position Post- Processing"]
    B --> F["Sensor Self-Calibration"]
    C --> G["Adjacent Key Suppresion™"]
    D --> H["Noise Counter Measure"]
    E --> I["Detect Integration Mechanism"]
    F --> J["Auto Re-Calibration"]
    G --> K["Program PTC registers"]
    H --> K
    I --> K
    J --> K
    K --> L["SAM D PTC Module"]
    L --> M["Raw sensor data"]
    M --> N["Sensor Touch Status Rotor/Slider Position"]

The QTouch Library API is arranged such that the user application can use standalone self-capacitance or mutual capacitance method or both methods, simultaneously. The following table captures the APIs available for each method. For normal operation, it is sufficient to use the set of Regular APIs for each method. The Helper APIs provides additional flexibility to the user application.

Method Regular API Helper API
Mutual capacitance	touch_muticap_sensors_inittouch_muticap_sensor_configtouch_muticap_sensors_calibratetouch_muticap_sensors_measuretouch_muticap_sensors_deinittouch_muticap_lowpower_sensor_enable_event_measure	touch_muticap_sensor_get_deltatouch_muticap_sensor_update_configtouch_muticap_sensor_get_configtouch_muticap_update_global_paramtouch_muticap_get_global_paramtouch_muticap_update_acq_configtouch_muticap_get_acq_configtouch_muticap_sensor_disabletouch_muticap_sensor_reenabletouch_muticap_mois_tolnce_enabletouch_multicap_mois_tolnce_disabletouch_muticap_cnfg_mois_thresholdtouch_muticap_cnfg_mois_mltchgrptouch_muticap_mois_tolnce_quick_reburst_enabletouch_muticap_mois_tolnce_quick_reburst_disabletouch_muticap_get_libinfotouch_library_get_version_info_touch_resume_ptctouch_suspend_ptc
Self-capacitance	touch_selfcap_sensors_inittouch_selfcap_sensor_configtouch_selfcap_sensors_calibratetouch_selfcap_sensors_measuretouch_selfcap_sensors_deinittouch_selfcap_lowpower_sensor_enable_event_measure	touch_selfcap_sensor_get_deltatouch_selfcap_sensor_update_configtouch_selfcap_sensor_get_configtouch_selfcap_update_global_paramtouch_selfcap_get_global_paramtouch_selfcap_update_acq_configtouch_selfcap_get_acq_configtouch_selfcap_sensor_disabletouch_selfcap_sensor_reenabletouch_selfcap_mois_tolnce_enabletouch_selfcap_mois_tolnce_disabletouch_selfcap_cnfg_mois_thresholdtouch_selfcap_cnfg_mois_mltchgrptouch_selfcap_mois_tolnce_quick_reburst_enabletouch_selfcap_mois_tolnce_quick_reburst_disabletouch_selfcap_get_libinfotouch_library_get_version_info.touch_suspend_ptctouch_resume_ptc

5.2. Library Parameters

The QTouch Library configuration parameters are listed in the following table:

Configuration	Mutual capacitance Self-capacitance
Pin Configuration	DEF_MUTCAP_NODES DEF_SELFCAP_LINES
Sensor Configuration DEF_MUTCAP_NUM_CHANNELS DEF_MUTCAP_NUM_SENSORSDEF_MUTCAP_NUM_ROTORS_SLIDERSDEF_MUTCAP_PTC_GPIO_STATEDEF_MUTCAP_QUICK_REBURST_ENABLE		DEF_SELFCAP_NUM_CHANNELS DEF_SELFCAP_NUM_SENSORSDEF_SELFCAP_NUM_ROTORS_SLIDERSDEF_SELFCAP_PTC_GPIO_STATEDEF_SELFCAP_QUICK_REBURST_ENABLE
Sensor Individual Parameters	Detect ThresholdDetect HysteresisPosition ResolutionPosition HysteresisAKS group	Detect ThresholdDetect HysteresisPosition ResolutionAKS group
Sensor Global Parameters DEF_MUTCAP_DI DEF_MUTCAP_TCH_DRIFT_RATEDEF_MUTCAPATCH_DRIFT_RATEDEF_MUTCAP_MAX_ON_DURATIONDEF_MUTCAP_DRIFT_HOLD_TIMEDEF_MUTCAPATCH_RECAL_DELAYDEF_MUTCAPATCH_RECAL_THRESHOLDDEF_MUTCAP_TOUCH_POSTPROCESS_MODEDEF_MUTCAP_AKS_ENABLE DEF_MUTCAP_CSDDEF_MUTCAP_AUTO_OS_SIGNAL_STABILITY_LIMIT	DEF_SELFCAP_DI DEF_SELFCAP_TCH_DRIFT_RATEDEF_SELFCAPATCH_DRIFT_RATEDEF_SELFCAP_MAX_ON_DURATIONDEF_SELFCAP_DRIFT_HOLD_TIMEDEF_SELFCAPATCH_RECAL_DELAYDEF_SELFCAPATCH_RECAL_THRESHOLDDEF_SELFCAP_TOUCH_POSTPROCESS_MODEDEF_SELFCAP_AKS_ENABLE DEF_SELFCAP_CSDDEF_SELFCAP_AUTO_OS_SIGNAL_STABILITY_LIMIT
Configuration Mutual capacitance Self-capacitance
Sensor Acquisition Parameters	DEF_MUTLCAP_FILTER_LEVEL_PER_NODEDEF_MUTLCAP_AUTO_OS_PER_NODEDEF_MUTLCAP_GAIN_PER_NODE DEF_MUTLCAP_FREQ_MODEDEF_MUTLCAP_HOP_FREQSDEF_MUTLCAP_CLK_PRESCALE_PER_NODEDEF_MUTLCAP_SENSE_RESISTOR_PER_NODE	DEF_SELFCAP_FILTER_LEVEL_PER_NODEDEF_SELFCAP_AUTO_OS_PER_NODEDEF_SELFCAP_GAIN_PER_NODE DEF_SELFCAP_FREQ_MODEDEF_SELFCAP_HOP_FREQSDEF_SELFCAP_CLK_PRESCALE_PER_NODEDEF_SELFCAP_SENSE_RESISTOR_PER_NODE
Sensor Calibration Auto Tune Setting	AUTO_TUNE_PRSC, AUTO_TUNE_RSEL, AUTO_TUNE_NONE	AUTO_TUNE_PRSC, AUTO_TUNE_RSEL, AUTO_TUNE_NONE
Sensor Noise measurement and Lockout Parameters	DEF_MUTLCAP_NOISE_MEAS_ENABLEDEF_MUTLCAP_NOISE_MEAS_SIGNAL_STABILITY_LIMITDEF_MUTLCAP_NOISE_LIMITDEF_MUTLCAP_NOISE_MEAS_BUFFER_CNTDEF_MUTLCAP_LOCKOUT_SELDEF_MUTLCAP_LOCKOUT_CNTLDOWN	DEF_SELFCAP_NOISE_MEAS_ENABLEDEF_SELFCAP_NOISE_MEAS_SIGNAL_STABILITY_LIMITDEF_SELFCAP_NOISE_LIMITDEF_SELFCAP_NOISE_MEAS_BUFFER_CNTDEF_SELFCAP_LOCKOUT_SELDEF_SELFCAP_LOCKOUT_CNTLDOWN
Sensor Acquisition Frequency Auto-tuning Parameters	DEF_MUTLCAP_FREQ_AUTO_TUNE_ENABLEDEF_MUTLCAP_FREQ_AUTO_TUNE_SIGNAL_STABILITY_LIMITDEF_MUTLCAP_FREQ_AUTO_TUNE_IN_CNT	DEF_SELFCAP_FREQ_AUTO_TUNE_ENABLEDEF_SELFCAP_FREQ_AUTO_TUNE_SIGNAL_STABILITY_LIMITDEF_SELFCAP_FREQ_AUTO_TUNE_IN_CNT
Common Parameters	DEF_TOUCH_MEASUREMENT_PERIOD_MS, DEF_TOUCH_PTC_ISR_LVL
Low Power Paramaters	DEF_LOWPOWER_SENSOR_EVENT_PERIODICITY, DEF_LOWPOWER_SENSOR_DRIFT_PERIODICITY_MS,DEF_LOWPOWER_SENSOR_ID
Moisture Parameters	DEF_MUTLCAP_MOIS_TOLERANCE_ENABLEDEF_MUTLCAP_NUM_MOIS_GROUPSDEF_MUTLCAP_MOIS_QUICK_REBURST_ENABLE	DEF_SELFCAP_MOIS_TOLERANCE_ENABLEDEF_SELFCAP_NUM_MOIS_GROUPSDEF_SELFCAP_MOIS_QUICK_REBURST_ENABLE

5.2.1. Pin, Channel, and Sensor Parameters

Mutual capacitance method uses a pair of sensing electrodes for each touch channel. These electrodes are denoted as X and Y lines. Capacitance measurement is performed sequentially in the order in which touch (X-Y) nodes are specified in the DEF_MUTLCAP_NODES configuration parameter. A mutual capacitance touch button sensor is formed using a single X-Y channel, while a touch rotor or slider sensor is formed using three to eight X-Y channels.

Mutual Capacitance Channel (X-Y Sense Node)

• SAM D20J and SAM D21J (64 pins): up to 256 touch channels, 16 X and 16 Y-lines
• SAM D20G and SAM D21G (48 pins): up to 120 touch channels, 12 X and 10 Y-lines
• SAM D20E and SAM D21E (32 pins): up to 60 touch channels, 10 X and 6 Y-lines
• SAM R21E(32 pins): up to 12 touch channels, 6 X and 2 Y-lines
• SAM R21G(48 pins) up to 48 touch channels, 8 X and 6 Y-lines
• SAM DA1J (64 pins): up to 256 touch channels, 16 X and 16 Y-lines
• SAM DA1G (48 pins): up to 120 touch channels, 12 X and 10 Y-lines
• SAM DA1E (32 pins): up to 60 touch channels, 10 X and 6 Y-lines
• SAM D21G17AU and SAM D21G18AU (45 pins): up to 132 touch channels, 12 X and 11 Y-lines
• SAM D21E15BU and SAM D21E16BU (35 pins): up to 60 touch channels, 10 X and 6 Y-lines

The following devices have X and Y multiplexing option.

• SAM D10C14A and SAM D11C14A (14 pins): up to 12 touch channels, 4 X and 3 Y-lines
• SAM D10D14 AS/AU and SAM D11D14 AS/AU (20 pins): up to 42 touch channels, 7 X and 6 Y-lines
• SAM D10D14AM and SAM D11D14AM (24 pins): up to 72 touch channels, 9 X and 8 Y-lines
• SAM L21E (32 pins): up to 42 touch channels, 7 X and 6 Y-lines
• SAM L21G (48 pins): up to 81 touch channels, 9 X and 9 Y-lines
• SAM L21J (64 pins): up to 169 touch channels, 13 X and 13 Y-lines

• SAM L22G (48 pins): up to 132 touch channels, 11 X and 12 Y-lines
• SAM L22J (64 pins): up to 182 touch channels, 13 X and 14 Y-lines
• SAM L22N (100 pins): up to 256 touch channels, 16 X and 16 Y-lines
- SAM C21E and SAM C20E(32 pins): up to 60 touch channels, 10 X and 6 Y-lines
• SAM C21G and SAM C20G(48 pins): up to 120 touch channels, 12 X and 10-Y lines
• SAM C21J and SAM C20J(64 pins): up to 256 touch channels, 16 X and 16 Y-lines
- ATmega328PB (32 pins): up to 144 touch channels, 12 X and 12 Y-lines
- ATmega324PB (44 pins): up to 256 touch channels, 16 X and 16 Y-lines

A few pins can be used either as X-line or Y-line. The datasheets of individual devices provide more information about this multiplexing option.

Figure 5-3. Mutual Capacitance Sensor Arrangement

graph LR
    A["PTC Module"] -->|X0| B["Cx,y0"]
    A -->|X1| C["Cx,y1"]
    A -->|Xn| D["Cx,yn"]
    A -->|Y0| E["Cx,y1"]
    A -->|Y1| F["Cx,yn"]
    A -->|Ym| G["Cx,y1"]
    H["Sensor Capacitance Cx,y"] --> I["Cx,y0"]
    H --> J["Cx,y1"]
    H --> K["Cx,yn"]

Figure 5-4. Mutual Capacitance - Channel to Sensor Mapping

graph TD
    subgraph Sensor_Inputs
        X0["Sensor 0 - Rotor/Slider"] --> Ch0["Ch 0"]
        X0 --> Ch1["Ch 1"]
        X0 --> Ch2["Ch 2"]
        X0 --> Ch3["Ch 3"]
    end
    subgraph Key_Cons
        Y2["Y2"] --> Ch4["Ch 4"]
        Y1["Y1"] --> Ch5["Ch 5"]
        Y0["Y0"] --> Ch6["Ch 6"]
        Y3["Y3"] --> Ch7["Ch 7"]
    end
    X0 --> Ch8["Ch 8"]
    X0 --> Ch9["Ch 9"]
    X0 --> Ch10["Ch 10"]
    X0 --> Ch11["Ch 11"]
    X0 --> Ch12["Ch 12"]
    X0 --> Ch13["Ch 13"]
    X0 --> Ch14["Ch 14"]
    X0 --> Ch15["Ch 15"]
    X0 --> Ch16["Ch 16"]
    X0 --> Ch17["Ch 17"]
    X0 --> Ch18["Ch 18"]
    X0 --> Ch19["Ch 19"]
    X0 --> Ch20["Ch 20"]
    X0 --> Ch21["Ch 21"]
    X0 --> Ch22["Ch 22"]
    X0 --> Ch23["Ch 23"]
    X0 --> Ch24["Ch 24"]
    X0 --> Ch25["Ch 25"]
    X0 --> Ch26["Ch 26"]
    X0 --> Ch27["Ch 27"]
    X0 --> Ch28["Ch 28"]
    X0 --> Ch29["Ch 29"]
    X0 --> Ch30["Ch 30"]
    X0 --> Ch31["Ch 31"]
    X0 --> Ch32["Ch 32"]
    X0 --> Ch33["Ch 33"]
    X0 --> Ch34["Ch 34"]
    X0 --> Ch35["Ch 35"]
    X0 --> Ch36["Ch 36"]
    X0 --> Ch37["Ch 37"]
    X0 --> Ch38["Ch 38"]
    X0 --> Ch39["Ch 39"]
    X0 --> Ch40["Ch 40"]
    X0 --> Ch41["Ch 41"]
    X0 --> Ch42["Ch 42"]
    X0 --> Ch43["Ch 43"]
    X0 --> Ch44["Ch 44"]
    X0 --> Ch45["Ch 45"]
    X0 --> Ch46["Ch 46"]
    X0 --> Ch47["Ch 47"]
    X0 --> Ch48["Ch 48"]
    X0 --> Ch49["Ch 49"]
    X0 --> Ch50["Ch 50"]
    X0 --> Ch51["Ch 51"]
    X0 --> Ch52["Ch 52"]
    X0 --> Ch53["Ch 53"]
    X0 --> Ch54["Ch 54"]
    X0 --> Ch55["Ch 55"]
    X0 --> Ch56["Ch 56"]
    X0 --> Ch57["Ch 57"]
    X0 --> Ch58["Ch 58"]
    X0 --> Ch59["Ch 59"]
    X0 --> Ch60["Ch 60"]
    X0 --> Ch61["Ch 61"]
    X0 --> Ch62["Ch 62"]
    X0 --> Ch63["Ch 63"]
    X0 --> Ch64["Ch 64"]
    X0 --> Ch65["Ch 65"]
    X0 --> Ch66["Ch 66"]
    X0 --> Ch67["Ch 67"]
    X0 --> Ch68["Ch 68"]
    X0 --> Ch69["Ch 69"]
    X0 --> Ch70["Ch 70"]
    X0 --> Ch71["Ch 71"]
    X0 --> Ch72["Ch 72"]
    X0 --> Ch73["Ch 73"]
    X0 --> Ch74["Ch 74"]
    X0 --> Ch75["Ch 75"]
    X0 --> Ch76["Ch 76"]
    X0 --> Ch77["Ch 77"]
    X0 --> Ch78["Ch 78"]
    X0 --> Ch79["Ch 79"]
    X0 --> Ch80["Ch 80"]
    X0 --> Ch81["Ch 81"]
    X0 --> Ch82["Ch 82"]
    X0 --> Ch83["Ch 83"]
    X0 --> Ch84["Ch 84"]
    X0 --> Ch85["Ch 85"]
    X0 --> Ch86["Ch 86"]
    X0 --> Ch87["Ch 87"]
    X0 --> Ch88["Ch 88"]
    X0 --> Ch89["Ch 89"]
    X0 --> Ch90["Ch 90"]
    X0 --> Ch91["Ch 91"]
    X0 --> Ch92["Ch 92"]
    X0 --> Ch93["Ch 93"]
    X0 --> Ch94["Ch 94"]
    X0 --> Ch95["Ch 95"]
    X0 --> Ch96["Ch 96"]
    X0 --> Ch97["Ch 97"]
    X0 --> Ch98["Ch 98"]
    X0 --> Ch99["Ch 99"]

X-Y node pair can be specified using the configuration parameter DEF_MUTLCAP_NODES in a non-sequential order. The channel numbering is done in the same order as the X-Y node pair specified in the configuration parameter DEF_MUTLCAP_NODES.

Setting Configuration Name Data Type Unit Min Max Typical
Mutual Cap Touch Channel Nodes	DEF_MUTLCAP_NODES uint16_t	array	None	1 X-Y node pair	256 X-Y nodepair	-
Mutual Cap Number of Channels	DEF_MUTLCAP_NUM_CHANNELS uint16_t		None	1 256 X-Y nodepair		-
Mutual Cap Number of Sensors	DEF_MUTLCAP_NUM_SENSORS uint16_t		None	1 256 X-Y nodepair		-
Mutual Cap Number of Rotors and Sliders	DEF_MUTLCAP_NUM_ROTORS_SLIDERS	uint8_t	None	0 85 node pair		-

Self-capacitance method uses a single sense electrode, denoted by a Y-line. Capacitance measurement is performed sequentially in the order in which Y-lines are specified in the DEF_SELFCAP_LINES configuration parameter. Self-capacitance touch button sensor is formed using a single - line channel, while a touch rotor or slider sensor can be formed using three Y-line channels.

Self-capacitance Channel (Y-sense line)

• SAM D20J and SAM D21J (64 pins): up to 16 channels
• SAM D20G and SAM D21G (48 pins): up to 10 channels
- SAM D20E and SAM D21E (32 pins): up to 6 channels
- SAM D10C14A and SAMD 11C14A (14 pins): up to 7 touch channels
- SAM D10D14 AS/AU and SAMD 11D14 AS/AU (20 pins): up to 13 touch channels
- SAM D10D14AM and SAMD 11D14AM (24 pins): up to 16 touch channels
• SAM L21E (32 pins): up to 7 touch channels
• SAM L21G (48 pins): up to 10 touch channels
• SAM L21J (64 pins): up to 16 touch channels
• SAMR21E (32 pins): up to 2 touch channels
- SAMR21G (48 pins): up to 6 touch channels
• SAM DA1J (64 pins): up to 16 channels
• SAM DA1G (48 pins): up to 10 channels
• SAM DA1E (32 pins): up to 6 channels
• SAM C21E and SAM C20E (32 pins): up to 16 touch channels
- SAM C21G and SAM C20G (48 pins): up to 22 touch channels
• SAM C21J and SAM C20J (64 pins): up to 32 touch channels
• SAM L22G (48 pins): up to 15 touch channels
• SAM L22J (64 pins): up to 19 touch channels
• SAM L22N (100 pins): up to 24 touch channels
- ATmega328PB (32 pins): up to 24 touch channels

- ATmega324PB (44 pins): up to 32 touch channels

Figure 5-5. Self-capacitance Sensor Arrangement

Sensor Capacitance Cy Yc Y1 PTC Module Cyt Cy1 .......... Cym

Figure 5-6. Self-capacitance Channel to Sensor Mapping

graph LR
    A["PTC Self Cap"] --> B["Y line 0"]
    A --> C["Y line 1"]
    A --> D["Y line 2"]
    A --> E["Y line 3"]
    B --> F["channel 0"]
    C --> G["channel 1"]
    D --> H["channel 2"]
    E --> I["channel 3"]
    F --> J["Sensor0"]
    G --> J
    H --> J
    I --> K["Sensor1"]

Y sense line can be specified using the configuration parameter DEF_SELFCAP_LINES in non-sequential order. The channel numbering is done in the same order as the Y sense line specified in the configuration parameter DEF_SELFCAP_LINES.

Setting Configuration Name		Data Type	Unit Min Max Typical
Self Cap touch channel nodes	DEF_SELFCAP_NODES uint16_t	array	None	1 Y-line	32 Y-line	-
Self Cap number of channels	DEF_SELFCAP_NUM_CHANNELS uint16_t		None	1 Y-line	32 Y-line	-
Self Cap number of Sensors	DEF_SELFCAP_NUM_SENSORS uint16_t		None	1 Y-line	32 Y-line	-
Self Cap number of Rotors and Sliders	DEF_SELFCAP_NUM_ROTORS_SLIDERS	uint8_t	None	0 Y-line	10 Y-line	-

The touch sensors must be enabled in the sequential order of the channels specified using the touch_xx_sensor_config() API. For improved EMC performance, a series resistor with value of 1 Kilo-ohm must be used on X and Y lines. For more information about designing the touch sensor, refer to Buttons, Sliders and Wheels Touch Sensor Design Guide available at www.atmel.com.

5.2.2. Sensor Individual Parameters

This section explains the settings that are specific to the individual sensor.

Detect Threshold

A sensor's detect threshold defines how much its signal must increase above its reference level to qualify as a potential touch detect. However, the final detection confirmation must satisfy the Detect Integrator (DI) limit. Larger threshold values desensitize sensors since the signal must change more (i.e. requires larger touch) to exceed the threshold level. Conversely, lower threshold levels make sensors more sensitive.

Threshold setting depends on the amount of signal swing when a sensor is touched. Usually, thicker front panels or smaller electrodes have smaller signal swing on touch, thus require lower threshold levels. Typically, detect threshold isset to 50% of touch delta. Desired touch delta for a buttons is \~30 to 80 counts and for wheels or sliders is \~50 to 120 counts.

Setting	Configuration Name	Data Type Unit	Min Max	Typical
Threshold	detect_threshold	threshold_t	Counts	3 255	20-50(For buttons)30-80(For sliders and wheels)

Detect Hysteresis

This setting is sensor detection hysteresis value. It is expressed as a percentage of the sensor detection threshold setting. Once a sensor goes into detect its threshold level is reduced (by the hysteresis value) in order to avoid the sensor dither in and out of detect if the signal level is close to original threshold level.

• Setting of 0 = 50% of detect threshold value (HYST_50)
• Setting of 1 = 25% of detect threshold value (HYST_25)
• Setting of 2 = 12.5% of detect threshold value (HYST_12_5)
• Setting of 3 = 6.25% of detect threshold value (HYST_6_25)

Setting	Configuration Name	Data Type Unit Min Max Typical
Hysteresis	detect_threshold uint8_t (2bits)	Enum	HYST_6_25	HYST_50	HYST_6_25

Position Resolution

The rotor or slider needs the position resolution (angle resolution in case of rotor and linear resolution in case of slider) to be set. Resolution is the number of bits needed to report the position of rotor or slider. It can have values from 2 bits to 8 bits.

Setting Configuration Name Data Type Unit Min Reported					Max Reported Position	Typical
Position Resolution	position_resolution	uint8_t (3bits)	None	2bits 0-3	8bits 0-25	8

Position Hysteresis

In case of Mutual Cap, the rotor or slider needs the position hysteresis (angle hysteresis in case of rotor and linear hysteresis in case of slider) to be set. It is the number of positions the user has to move back, before touch position is reported when the direction of scrolling is changed and during the first scrolling after user press.

Hysteresis can range from 0 (1 position) to 7 (8 positions). The hysteresis is carried out at 8 bits resolution internally and scaled to desired resolution; therefore at resolutions lower than 8 bits there might be a difference of 1 reported position from the hysteresis setting, depending on where the touch is detected. At lower resolutions, where skipping of the reported positions is observed, hysteresis can be set to 0 (1 position). At Higher resolutions (6 to 8bits), it would be recommended to have a hysteresis of at least 2 positions or more.

Note: It is not valid to have a hysteresis value more than the available bit positions in the resolution. For instance, a hysteresis value of 5 positions with a resolution of 2 bits (4 positions) is invalid. Position hysteresis is invalid (unused) in case of self-capacitance method sensors.

Setting Configuration Name Data Type Unit Min Max Typical
Position Hysteresis	position_hysteresis	uint8_t (3bits)	-	0	7	8

Adjacent Key Suppression (AKS®)

In designs where the sensors are close together or configured for high sensitivity, multiple sensors might report a detect simultaneously. To allow applications to determine the intended single touch, the touch library provides the user the ability to configure a certain number of sensors in an AKS group.

When a group of sensors are in the same AKS group, only the first strongest sensor will report detection. The sensor reporting detection will continue to report detection even if another sensor's delta becomes stronger. The sensor stays indetect until its delta falls lower than its detection threshold. If any more sensors in the AKS group are still in detect only the strongest will report detection. At a given time point, only one sensor from each AKS group is reported to be indetect.

AKS feature can be enabled or disabled using a macro DEF_XXXXCAP_AKS_ENABLE

• 1u = AKS grouping functionality is enabled
• 0u = AKS grouping functionality is disabled

The library provides the ability to configure a sensor to belong to one of the Adjacent Key Suppression Groups (AKS Group).

5.2.3. Sensor Global Parameters

This section explains the settings that are common all sensors. For instance, if recalibration threshold (one of the global settings) of mutual cap sensors is set as RECAL_100, all mutual capacitance sensors will be configured for a recalibration threshold of 100%. These sensor global parameter settings can be independently set to self-capacitance and mutual capacitance sensors.

Detect Integration

The QTouch Library features a detect integration mechanism, which confirm detection in a robust environment. The detect integrator (DI) acts as a simple signal filter to suppress false detections caused by spurious events such as electrical noise.

A counter is incremented each time the sensor delta has exceeded its threshold and stayed there for a specific number of acquisitions, without going below the threshold levels. When this counter reaches a preset limit (the DI value) the sensor is finally declared to be touched. If on any acquisition the delta is below the threshold level, the counter is cleared and the process has to start from the beginning. The DI process is applicable to a 'release' (going out of detect) event as well.

For example, if the DI value is 10, the device has to exceed its threshold and stay there for (10 + 2) successive acquisitions without going below the threshold level, before the sensor is declared to be touched.

Setting Configuration Name Data Type Unit Min Max Typical
DI DEF_MUTLCAP_DI, DEF_SELFCAP_DI		uint8_t	Cycles 0	255 4

Max-ON Duration

If an object unintentionally contacts a sensor resulting in a touch detection for a prolonged interval it is usually desirable to recalibrate the sensor in order to restore its function, after a time delay of a few seconds.

The Maximum ON duration timer monitors such detections; if detection exceeds the timer's settings, the sensor is automatically recalibrated. After a recalibration has taken place, the affected sensor once again functions normally even if it still in contact with the foreign object.

Max-ON duration can be disabled by setting it to zero (infinite timeout) in which case the channel never recalibrates during a continuous detection (but the host could still command it).

Setting Configuration Name Data Type Unit Min Max Typical
Maximum ON Duration	DEF_MUTLCAP_MAX_ON_DURATION,DEF_SELFCAP_MAX_ON_DURATION	uint8_t	200ms	0	255	30(6s)

Away from Touch and Towards Touch Drift Rate

Drift in a general sense means adjusting reference level (of a sensor) to allow compensation for temperature (or other factor) effect on physical sensor characteristics. Decreasing reference level for such compensation is called Negative drift & increasing reference level is called Positive drift. Specifically, the drift compensation should be set to compensate faster for increasing signals than for decreasing signals.

Signals can drift because of changes in physical sensor characteristics over time and temperature. It is crucial that such drift be compensated for; otherwise false detections and sensitivity shifts can occur.

Drift compensation occurs only while there is no detection in effect. Once a finger is sensed, the drift compensation mechanism ceases since the signal is legitimately detecting an object. Drift compensation works only when the signal inquestion has not crossed the 'Detect threshold' level.

The drift compensation mechanism can be asymmetric. It can be made to occur in one direction faster than it does in the other simply by changing the appropriate setup parameters.

Signal values of a sensor tend to increase when an object (touch) is approaching it or a characteristic change of sensor over time and temperature. Increasing signals should not be compensated quickly, as an approaching finger could be compensated for partially or entirely before even touching the channel (towards touch drift).

However, an object over the channel which does not cause detection, and for which the sensor has already made full allowance (over some period of time), could suddenly be removed leaving the sensor with an artificially suppressed reference level and thus become insensitive to touch. In the latter case, the sensor should compensate for the object's removal by raising the reference level relatively quickly (away from touch drift).

Setting Configuration Name Data Type Unit Min Max Typical
Towards touch Drift	DEF_MUTLCAP_TCH_DRIFT_RATE,DEF_SELFCAP_TCH_DRIFT_RATE	uint8_t	200ms	0	127	20(4s)
Away from touch Drift	DEF_MUTLCAPATCH_DRIFT_RATE,DEF_SELFCAPATCH_DRIFT_RATE	uint8_t	200ms	0	127	5(1s)

Drift Hold Time

Drift Hold Time (DHT) is used to restrict drift on all sensors while one or more sensors are activated. It defines the length of time the drift is halted after a key detection. This feature is useful in cases of high density keypads where touching a key or floating a finger over the keypad would cause untouched keys to drift, and therefore create a sensitivity shift, and ultimately inhibit any touch detection.

Setting Configuration Name Data Type Unit Min Max Typical
Drift Hold Time	DEF_MUTLCAP_DRIFT_HOLD_TIME,DEF_SELFCAP_DRIFT_HOLD_TIME	uint8_t	200ms	0	255	20(4s)

Away From Touch Recalibration Threshold

Recalibration threshold is the level beyond which automatic recalibration occurs. Recalibration threshold is expressed as a percentage of the detection threshold setting.

This setting is an enumerated value and its settings are as follows:

• Setting of 0 = 100% of detect threshold (RECAL_100)
• Setting of 1 = 50% of detect threshold (RECAL_50)
• Setting of 2 = 25% of detect threshold (RECAL_25)
• Setting of 3 = 12.5% of detect threshold (RECAL_12_5)
• Setting of 4 = 6.25% of detect threshold (RECAL_6_25)

However, an absolute value of 4 is the hard limit for this setting. For example, if the detection threshold is, 40 and the Recalibration threshold value is set to 4.

Although this implies an absolute value of 2 (40 * 6.25% = 2.5), it is hard limited to 4.

Setting Configuration Name Data Type Unit Min Max Typical
Recalibration threshold	DEF_MUTLCAP_ATCH_RECAL_THRESHOLD,DEF_SELFCAP_ATCH_RECAL_THRESHOLD	uint8_t	Enum	RECAL_6_25	Detect threshold	RECAL_100

Away From Touch Recalibration Delay

If any key is found to have a significant negative delta, it is deemed to be an error condition. If this condition persists for more than the away from touch recalibration delay, i.e., qt_pos_recal_delay period, then an automatic recalibration is carried out.

A counter is incremented each time the sensor delta is equal to the away from touch recalibration threshold and stayed there for a specific number of acquisitions. When this counter reaches a preset limit (the PRD value) the sensor is finally recalibrated. If on any acquisition the delta is seen to be greater than the away from touch recalibration threshold level, the counter is cleared and the away from touch drifting is performed.

For example, if the away from touch recalibration delay setting is 10, then the delta has to drop below the recalibration threshold and stay there for 10 acquisitions in succession without going below the threshold level, before the sensor is declared to be recalibrated. Away from touch recalibration can be disabled with a setting of 0.

Setting Configuration Name Data Type Unit Min Max Typical
Away from touch Recalibration Delay	DEF_MUTLCAP_ATCH_RECAL_DELAY,DEF_SELFCAP_ATCH_RECAL_DELAY	uint8_t	Cycles	0	255	10

Sensor Post-Processing Mode

When TOUCH_LIBRARY_DRIVEN mode is selected, the library self-initiates repeated touch measurements to resolve touch press, release and calibration. This mode is suited for best response time.

When TOUCH_APPLN_DRIVEN mode is selected, the library does not initiate repeated touch measurement to resolve touch press, release and calibration. This mode suits deterministic PTC interrupt execution time for applications requiring stringent CPU time requirements. As repeated touch measurements are delayed due to other critical application code being executed. This mode can potentially affect the touch response time.

In order to improve the touch response time with the TOUCH_APPLN_DRIVEN mode, the touch_xxxcap_sensors_measure API call should be modified as below to initiate touch measurements periodically or when the burst again acquisition status flag has been set.

if ((touch_time.time_to_measure_touch == 1u) || (p_mutlcap_measure_data->acq_status & TOUCH_BURST_AGAIN)
    {
    /* Start a touch sensors measurement process. */
    touch_ret =
    touch_mutlcap_sensors_measure(touch_time.current_time_ms, NORMAL_ACQ_MODE, touch_mutlcap_measure 

complete_callback); 

Setting Configuration Name Data Type Options Typical
Sensor post-processing mode	DEF_MUTLCAP_TOUCH_POSTPROCESS_MODE,DEF_SELFCAP_TOUCH_POSTPROCESS_MODE	uint16_t	TOUCH_LIBRARY_DRIVEN,TOUCH_APPLN_DRIVEN	TOUCH_LIBRARY_DRIVEN

Charge Share Delay

Charge share delay indicates the number of additional charge cycles that are inserted within a capacitance measurement cycle to ensure that the touch sensor is fully charged. The CSD value is dependent on the sensor capacitance along with the series resistor on the Y line.

Note: Any increase in the charge share delay also increases the measurement time for a specific configuration.

When manual tuning is performed, the CSD value for the sensor with largest combination of capacitance along with series resistance should be considered.

Setting Configuration Name Data Type Options Min Max Typical
CSD (Charge Share Delay)	DEF_MUTL_CAP_CSD_VALUE,DEF_SELF_CAP_CSD_VALUE	uint8_t	PTC cycles 0 250 0

How to tune the CSD setting manually?

1. Initially, use an arbitrarily large value such as 64 and note the signal value. A large value ensures that the charge time is enough for full charge transfer
2. Reduce the CSD and verify the signal value drop, until signal is approximately 97-98% of the value used initially. This ensures a good charge transfer without any major loss in the signal.
3. Continue the same procedure [Step 1 and 2] for all the sensors available in the system. Use the largest value of the CSD used in the system for the global setting.

Note: For the same CSD setting, Mutual capacitance has a lower burst time than self-capacitance. A unit increase in mutual capacitance CSD consumes around 12 PTC cycles. Whereas for the self-capacitance an increase in CSD consumes approximately twice the mutual capacitance CSD time with the same setting.

Auto-OS Signal Stability Limit

The parameter DEF_XXXXCAP_AUTO_OS_SIGNAL_STABILITY_LIMIT defines the stability limit of the signals for performing over-samples. Stability limit is the variance in sensor signal value under noisy environment. A high level of stability limit is set to auto trigger oversamples on large noise presence. It is recommended to keep this setting close to the lowest sensor detect threshold of the system and tune it further based on the noise.

Range: 1 to 1000

5.2.4. Sensor Acquisition Parameters

Filter Level

The filter level setting controls the number of samples taken to resolve each acquisition. A higher filter level setting provides improved signal to noise ratio under noisy conditions, while increasing the total time

for measurement resulting in increased power consumption and response time. This setting is available on per channel basis, allowing easy tuning.

Setting Configuration Name Data Type Options Min Max Typical
Filter level	DEF_MUTCAP_FILTER_LEVEL_PER_NODE,DEF_SELFCAP_FILTER_LEVEL_PER_NODE	filter_level_t	Number of samples 1 64 16

Auto Oversamples

Auto oversample controls the automatic oversampling of sensor channels when unstable signals are detected with the default setting of 'Filter level'. Enabling Auto oversample results in 'Filter level' x 'Auto Oversample' number of samples taken on the corresponding sensor channel when an unstable signal is observed. In a case where 'Filter level' is set to FILTER_LEVEL_4 and 'Auto Oversample' is set to AUTO_OS_4, 4 oversamples are taken with stable signal values and 16 oversamples are taken when unstable signal is detected. This setting is available on per channel basis, allowing easy tuning.

A higher filter level setting provides improved signal to noise ratio under noisy conditions, while increasing the total time for measurement resulting in increased power consumption and response time.

Figure 5-7. Auto oversamples

graph TD
    A["Channel Measurement\n(Based on Filter_Level configuration)"] --> B{Compare to Previous Measurements}
    B -->|Unstable| C["Channel Measurement\n(Based on the Filter_Level and Auto_OS Settings)"]
    B -->|Stable| D["Measurement Complete"]
    C --> D
    D --> E["Post Processing"]

Auto oversamples can be disabled to obtain best power consumption.

Setting Configuration Name Data Type Options Min Max Typical
Auto Oversamples	DEF_MUTCAP_AUTO_OS_PER_NODE,DEF_SELFCAP_AUTO_OS_PER_NODE	auto_os_t Sample multiplier	2 128		AUTO_OS_NONE

Gain Setting

Gain setting is applied on a per-channel basis to allow a scaling-up of the touch delta upon contact. Gain setting depends on the sensor design and touch panel thickness.

Setting	Configuration Name	Data Type	Options	Min	Max	Typical
Gain	DEF_MUTCAP_GAIN_PER_NODE,DEF_SELFCAP_GAIN_PER_NODE	gain_t	Gain multiplier 1	32	1 (For self-capacitance) 4 (For mutual capacitance)

The figure shows the expected signal value for a given combination of gain setting and filter level setting. The values provided are only indicative and the actual sensor signal values might be close to the suggested levels.

Figure 5-8. Average Settling Signal Value for FILTER LEVEL and GAIN Combination

S_Gain = Software Gain [Digital Gain] and H_Gain = Hardware Gain [Analog gain]
Average settling Signal value for FILTER LEVEL and GAIN combination	GAIN_1		GAIN_2		GAIN_4		GAIN_8		GAIN_16	GAIN_32
FILTER_LEVEL_1	512		512		512		512		512	512
	S_Gain = 0	H_Gain = 0	S_Gain = 0	H_Gain = 1	S_Gain = 0	H_Gain = 2	S_Gain = 0	H_Gain = 3	S_Gain = 0	H_Gain = 4
FILTER_LEVEL_2	512		1024		1024		1024		1024	1024
	S_Gain = 0	H_Gain = 0	S_Gain = 1	H_Gain = 0	S_Gain = 1	H_Gain = 1	S_Gain = 1	H_Gain = 2	S_Gain = 1	H_Gain = 3
FILTER_LEVEL_4	512		1024		2048		2048		2048	2048
	S_Gain = 0	H_Gain = 0	S_Gain = 1	H_Gain = 0	S_Gain = 2	H_Gain = 0	S_Gain = 2	H_Gain = 1	S_Gain = 2	H_Gain = 2
FILTER_LEVEL_8	512		1024		2048		4096		4096	4096
	S_Gain = 0	H_Gain = 0	S_Gain = 1	H_Gain = 0	S_Gain = 2	H_Gain = 0	S_Gain = 3	H_Gain = 0	S_Gain = 3	H_Gain = 1
FILTER_LEVEL_16	512		1024		2048		4096		8192	8192
	S_Gain = 0	H_Gain = 0	S_Gain =1	H_Gain = 0	S_Gain =2	H_Gain = 0	S_Gain =3	H_Gain = 0	S_Gain = 4	H_Gain = 0
FILTER_LEVEL_32	512		1024		2048		4096		8192	16984
	S_Gain = 0	H_Gain = 0	S_Gain=1	H_Gain = 0	S_Gain =2	H_Gain = 0	S_Gain =3	H_Gain = 0	S_Gain = 4	H_Gain = 0
FILTER_LEVEL_64	512		1024		2048		4096		8192	16984
	S_Gain = 0	H_Gain = 0	S_Gain=1	H_Gain = 0	S_Gain = 2	H_Gain = 0	S_Gain =3	H_Gain = 0	S_Gain = 4	H_Gain = 0
RECOMMENDATIONS	EXCELLENT						GOOD		POOR

Prescalar Setting

The prescaler parameter denotes the clock divider for the particular channel. It can be set on per channel basis and is independent to each sensor node/channel. This parameter is auto tuned based on the auto tune settings. Tuning this parameter allows for improved noise performance.

Setting Configuration Name Data Type Options Min Max Typical
Prescalar	DEF_MUTLCAP_CLK_PRESCALE_PER_NODE,DEF_SELPCAP_CLK_PRESCALE_PER_NODE	prsc_div_sel_t	PRSC_DIV_SEL_1,PRSC_DIV_SEL_2,PRSC_DIV_SEL_4,PRSC_DIV_SEL_8	PRSC_DIV_SEL_1	PRSC_DIV_SEL_6	PRSC_DIV_SEL_1

Series Resistor Setting

The series resistor denotes the resistor used on the particular channel for the acquisition. The value is tunable and allows both auto and manual tuning options. Tuning this parameter allows for improved noise performance.

Setting	Configuration Name Data Type Options Min Max Typical
Series Resist or	DEF_MUTICAP_SENSE_RESTSTOR_PER_NODEDEF_SELTCAP_SENSE_RESTSTOR_PER_NODE.	rsel_val_t	RSEL_VAL_0,RSEL_VAL_20,RSEL_VAL_50,RSEL_VAL_100	RSET_VAL_0	RSEL_VAL_100	RSET_VAL_100

Boot Prescalar Setting

The boot prescaler parameter denotes the clock divider for the particular channel. It can be set on per channel basis and is independent to each sensor node/channel. This setting is used for calibrating the sensors after a power-on. This parameter must be configured as the auto tune is not available.

Setting Configuration Name Data Type Options Min Max Typical
Boot Prescalar	DEF_MUTLCAP_CC_CAL_CLK_PRESCALE_PER_NODE, DEF_SELFCAP_CC_CAL_CLK_PRESCALE_PER_NODE	prsc_div_sel_t	PRSC_DIV_SEL_1, PRSC_DIV_SEL_2, PRSC_DIV_SEL_4, PRSC_DIV_SEL_6	PRSC_DIV_SEL_1	PRSC_DIV_SEL_8	PRSC_DIV_SEL_1

Boot Series Resistor Setting

The boot series resistor denotes the resistor used on the particular channel on device power-on calibration. This parameter must be configured as the auto tune is not available.

Setting	Configuration Name Data Type Options Min Max Typical
Boot Series Resistor	DEF_MUTLCAP_CC_CAL_SENSE_RESISTOR_PER_NODE	rsel_val_t	RSEL_VAL_0, RSEL_VAL_20, RSEL_VAL_50, RSEL_VAL_130	RSEL_VAL_0	RSEL_VAL_100	RSEL_VAL_130

Frequency Mode

Frequency mode setting allows users to tune the PTC touch acquisition frequency characteristics to counter environment noise.

FREQ\_MODE\_HOP

When frequency mode hopping option is selected, the PTC runs a frequency hopping cycle with subsequent measurements done using the three PTC acquisition frequency delay settings as specified in DEF_SELFCAP_HOP_FREQS. In this case, an additional software median filter is applied to the measured signal values.

FREQ\_MODE\_SPREAD

When frequency mode spread spectrum option is selected, the PTC runs with spread spectrum enabled for jittered delay based acquisition.

FREQ\_MODE\_SPREAD\_MEDIAN

When frequency mode spread spectrum median option is selected, the PTC runs with spread spectrum enabled. In this case, an additional software median filter is applied to the measured signal values.

FREQ\_MODE\_NONE

When frequency mode none option is selected, the PTC runs at constant speed. This mode is suited for best power consumption.

Setting Configuration Name Data Type	Options		Min Max		Typical
Frequency mode	DEF_MUTLCAP_FREQ_MODE, DEF_SELFCAP_FREQ_MODE	freq_mode_sel_t	FREQ_MODE_NONE, FREQ_MODE_TOP, FREQ_MODE_SPREAD, FREQ_MODE_SPREAD_MEDIAN	FREQ_MODE_NONE	FREQ_MODE_SPREAD_MEDIAN FREQ_MODE_NONE

Frequency Hop Delay

The frequency hop delay setting is used when the Frequency mode is set to FREQ_MODE_HOP. A set of three frequency hop delay settings should be specified. This delay setting inserts n PTC clock cycles between consecutive measurements on a given sensor, thereby changing the PTC acquisition frequency. FREQ_HOP_SEL_1 setting inserts 0 PTC clock cycle between consecutive measurements.

FREQ_HOP_SEL_16 setting inserts 15 PTC clock cycles. Hence, higher delay setting will increase the total time taken for capacitance measurement on a given sensor as compared to a lower delay setting. A desired setting can be used to avoid noise around the same frequency as the acquisition frequency.

Setting Configuration Name Data Type Unit Min		Max Typical
Frequency hop delay	DEF_MUTLCAP_HOP_FREQS, DEF_SELFCAP_HOP_FREQS	freq_hop_sel_t nPTC_clock_cycles FREQ_HOP_SEL_1 FREQ_HOP_SEL_16	FREQ_HOP_SEL_1, FREQ_HOP_SEL_2, FREQ_HOP_SEL_3

5.2.5. Sensor Calibration Auto Tune Setting

Auto tune parameter setting is passed to the touch_xx_sensors_calibrate API in order to allow users to tune the PTC module for power consumption or noise performance.

AUTO\_TUNE\_PRSC

When Auto tuning of pre-scaler is selected, the PTC uses the user defined internal series resistor setting (DEF_XXXXCAP_SENSE_RESISTOR_PER_NODE) and the pre-scaler is adjusted to slow down the PTC operation to ensure full charge transfer. Auto tuning of pre-scaler with RSEL_VAL_100 as the series resistor results in least power consumption while resulting in increased power consumption and touch response time.

AUTO\_TUNE\_RSEL

When Auto tuning of the series resistor is selected, the PTC runs at user defined pre-scaler setting speed (DEF_XXXXCAP_CLK_PRESCALE_PER_NODE) and the internal series resistor is tuned automatically to the optimum value to allow for full charge transfer. Auto tuning of series resistor with PRSC_DIV_SEL_1 as the PTC pre-scale results in best case power consumption.

AUTO\_TUNE\_NONE

When manual tuning option is selected, the user defined values of PTC pre-scaler and series resistor is used for PTC operation as given in DEF_XXXXCAP_CLK_PRESCALE_PER_NODE and DEF_XXXXCAP_SENSE_RESISTOR_PER_NODE

Setting	Configuration Name Data Type Unit Values Typical
Auto tune Provided to touch_xxcap_sensors_calibrate API input	auto_tune_type_t	None AUTO_TUNE_NONE, AUTO_TUNE_PRSC,AUTO_TUNE_RSEL	AUTO_TUNE_NONE

5.2.6. Sensor Noise Measurement and Lockout Parameters

Noise is measured on a per-channel basis after each channel acquisition, using historical data on a rolling window of successive measurements. Reported noise to exclude the instance of an applied or removed touch contact, but the noise indication must react sufficiently fast that false touch detection before noise lockout is prevented.

Signal change from sample to sample during the window buffer is compared to the stability limit. Noise is reported only when two changes occur within the window period and both of which exceed the DEF_XXXXCAP_NOISE_MEAS_SIGNAL_STABILITY_LIMIT limit.

Noise is calculated using the following algorithm:

if (swing count > 2)
    {
    Nk = ((|Sn - Sn-1| > DEF_XXXXCAP_NOISE_MEAS_SIGNAL_STABILITY)) ? (0) : (|Sn-Sn-1| - DEF_XXXXCAP_NOISE_MEAS_SIGNAL_STABILITY))
    }
else
    {
    Nk = 0
    } 

The swing count is number of signal changes that exceed

DEF MUTLCAP NOISE MEAS SIGNAL STABILITY LIMIT limit during buffer window period.

When the measured noise exceeds DEF_MUTLCAP_NOISE_LIMIT, the touch library locks out sensors, reports no touch detection and drifting is stopped. Noise measurement is provided for all the channels.

Each byte in p_xxxxcap_measure_data-> p_nm_ch_noise_val provides the noise level associated with that channel. Noise indication is provided for all the sensors configured by the application.

A bit is available in p_xxxxcap_measure_data->p_sensor_noise_status for each sensor to determine whether the sensor is noisy or not. The following code snippet provides the sample code to read the noise status of a particular sensor.

Figure 5-9. Noise Calculation

graph TD
    A["Normal measurement"] --> B{Noise Meas = ENABLE}
    B -->|Yes| C["Calculate Noise level"]
    B -->|No| D{Global lockout == Enable}
    C --> D
    D -->|No| E{Single key lockout = Enable}
    D -->|Yes| F{noise value > noise limit && Lockout sensor = noisy}
    E -->|Yes| G{Current noise > prev_noise}
    E -->|No| H["Decrement Lockout Countdown"]
    G -->|Yes| I{Noise value > Noise limit && {}
    G -->|No| J["Decrement the noise value"]
    I --> K{Lockout Count = 0}
    K -->|yes| L["Clear lock Bit for all sensor"]
    K -->|No| M["Set Lockout bit for all sensor and Initialize Lockout countdown with MAX value"]
    L --> M
    M --> N["Sensor Post processing"]
    E --> O{Noise value < Noise limit}
    O -->|yes| P["Clear unlock Bit for current sensor"]
    O -->|No| M
    P --> Q["Set Lockout bit for current sensor and Limit current Noise value = 2 * Noise limit."]

Noise Measurement Signal Stability Limit

The parameter DEF_XXXXAP_NOISE_MEAS_SIGNAL_STABILITY_LIMIT is the variance in sensor signal value under noisy environment. Any noise level over and above the noise signal stability limit contributes to the Noise limit.

It is recommended to keep this setting close to the lowest sensor detect threshold of the system and tune it further based on the noise.

Signal values can change from sample to sample during a window buffer period. The difference between adjacent buffer value is compared to the user configured stability limit.

Noise is reported only when two changes occur within the specified window period and only if both of which exceed the stability limit.

Range: 1 to 1000

Noise Limit

The DEF_XXXXCAP_NOISE_LIMIT specifies the limit to the total noise accumulated over the noise buffer count. If the accumulated noise exceeds the noise limit, then lockout is triggered. There are two purposes for this parameter:

• If the noise level calculated during a running window exceeds DEF_XXXXCAP_NOISE_LIMIT, then the corresponding sensor are declared noisy and sensor global noisy bit is set as '1'.
• If the noise level calculated during a running window exceeds DEF_XXXXCAP_NOISE_LIMIT, then system triggers the sensor lockout functionality.

Range: 1 to 255

Noise Measurement Buffer Count

The DEF_XXXXCAP_NOISE_MEAS_BUFFER_CNT parameter is used to select the buffer count for noise measurement buffer.

Range: 3 to 10 (If N number of samples differences have to be checked, define this parameter as "N + 1") If N = 4 then set DEF_XXXXCAP_NOISE_MEAS_BUFFER_CNT as 5u.

Sensor Lockout Selection

This feature locks out the sensors when the measured noise exceeds DEF_XXXXCAP_NOISE_LIMIT and does not report a touch. This prevents post-processing. So, the high level of noise cannot cause the channel to report false touch drift or recalibrate incorrectly.

The DEF_XXXXCAP_LOCKOUT_SEL parameter is used to select the lockout functionality method.

• If DEF_XXXXCAP_LOCKOUT_SEL is set to SINGLE_SENSOR_LOCKOUT and a sensor's noise level is greater than DEF_XXXXCAP_NOISE_LIMIT, then corresponding sensor is locked out from touch detection and drifting is disabled.
• If DEF_XXXXCAP_LOCKOUT_SEL is set to GLOBAL_SENSOR_LOCKOUT and any sensor's noise level is greater than DEF_XXXXCAP_NOISE_LIMIT, then all sensors are locked out from touch detection and drifting is disabled.
• If DEF XXXCAP_LOCKOUT_SEL is set to NO_LOCKOUT, then lockout feature is disabled.

Note: Global sensors noisy bit will be available for SINGLE_SENSOR_LOCKOUT and GLOBAL_SENSOR_LOCKOUT. Global sensors noisy bit will not be available for NO_LOCK_OUT.

Range: 0 to 2

Sensor Lockout Countdown

If the sensor signal moves from noisy to a good condition and stays there for a DEF_XXXXCAP_LOCKOUT_CNTDOWN number of measurements, the sensor is unlocked and sensors are ready for touch detection and drifting is enabled.

Note: This parameter is valid only for global lockout.

Range: 1 to 255

5.2.7. Sensor Acquisition Frequency Auto Tuning Parameters

The Frequency Auto Tune feature provides the best quality of signal data for touch detection by automatically selecting acquisition frequencies showing the best SNR in FREQ_MODE_HOP mode. During each measurement cycle, the signal change since the last acquisition at the same frequency is recorded for each sensor. After the cycle, when all sensors have been measured at the present acquisition frequency, the largest signal variation of all sensors is stored as the variance for that frequency stage.

The variance for each frequency stage is compared to the DEF_XXXXCAP_FREQ_AUTO_SIGNAL_STABILITY_LIMIT limit, and if the limit is exceeded, a per-stage counter is incremented. If the measured variance is lower than the limit, the counter is decremented, if it has not been set as zero. If all frequencies display noise exceeding the stability limit, only the counter for the specific frequency stage with the highest variance is incremented after its cycle.

When a frequency counter reaches the DEF_XXXXCAP_FREQ_AUTO_TUNE_IN_CNT (auto-tune count in variable), that frequency stage is selected for auto-tuning. A new frequency selection is applied and the counters and variances for all frequencies are reset. After a frequency has been selected for auto-tuning, the count-in for that frequency stage is set to half the original count-in and the process is repeated until either all frequencies have been measured or a frequency is selected which does not re-trigger auto-tuning is determined.

If all frequencies have been tested, and the variation exceeds the

DEF_XXXXCAP_FREQ_AUTO_SIGNAL_STABILITY_LIMIT limit then the frequency with the lowest variance is selected for the frequency stage currently under tuning. The auto-tune process is re-initialized and further tuning does not take place until a frequency stage's high variance counter again reaches the count in limit.

Figure 5-10. Frequency Auto Tune

graph TD
    A["Normal measurement"] --> B{(FREQ_HOP_MODE = ENABLE) && (FREQ_AUTO_TUNE = ENABLE)}
    B -->|No| C["Increment Frequency auto tune in count for this frequency"]
    B -->|Yes| D{Signal change of current freq > Stability limit}
    D -->|No| E["Decrement Auto tune counter"]
    D -->|Yes| F["Increment Frequency auto tune in count for this frequency"]
    F --> G{Auto tune in count > Auto tune_Limit}
    G -->|No| C
    G -->|Yes| H["Find the good Frequency and set as current frequency."]
    H --> I["Noise measurement and System post processing"]
    I --> C

Frequency Auto Tune Signal Stability

The DEF_XXXXCAP_FREQ_AUTO_SIGNAL_STABILITY_LIMIT is the variance in sensor signal value under noisy environment. A signal stability limit level is set to auto tune acquisition frequency on noise presence. It is recommended to keep this setting close to the lowest sensor detect threshold of the system and tune it further based on the noise.

Range: 1 to 1000

Frequency Auto Tune in Counter

The DEF_XXXXCAP_FREQ_AUTO_TUNE_IN_CNT parameter is used to trigger the frequency auto tune. If sensor signal change at each frequency exceeds the value specified as

DEF XXXCAP FREQ AUTO SIGNAL STABILITY LIMIT for

DEF_XXXXCAP_FREQ_AUTO_TUNE_IN_CNT, then frequency auto tune will be triggered at this frequency.

Range: 1 to 255

Note: The Frequency Auto Tune feature and related parameters are available only in FREQ_MODE_HOP mode.

5.2.8. Quick Re-burst Parameter

Quick Reburst

This macro is used to enable or disable quick re-burst feature. When Quick re-burst is enabled, upon user touch and release, only that touched sensor or channel is subsequently measured to resolve detect integration (or debounce). Enabling this feature results in best touch response time.

When Quick re-burst is disabled, upon user touch and release, all sensors or channels are measured to resolve detect integration (or debounce). This feature should only be disabled when developing any special application involving all sensor measurements during user activity.

Within an AKS (Adjacent Key suppression) group, all the sensors within that group are measured during user touch independent of this feature being enabled or disabled.

5.2.9. Common Parameters

Measurement Period

The measurement period setting is used to set the periodic interval for touch sensor measurement. The minimum measurement period setting should be greater than the time taken to complete measurement on all sensors. This can be simply determined by calling the touch_xx_sensors_measure API in a while loop and then toggling a GPIO pin in the measurement complete callback.

main()
{
    while(1)
    {
    touch_ret =
    touch_mutlcap_sensors_measure(touch_time.current_time_ms, NORMAL_ACQ_MODE, touch_mutlcap_measure_complete_callback);
    }
}

void touch_mutlcap_measure_complete_callback(void)
{
    if (!(p_mutlcap_measure_data->acq_status & TOUCH_BURST_AGAIN))
    {
    /* Set the Mutual Cap measurement done flag. */
    p_mutlcap_measure_data->measurement_done_touch = 1u;
    port_pin_toggle_output_level(PIN_PB00);
    }
} 

Setting Configuration Name Data Type Unit Values Max Typical
Sensor measurement interval	DEF_TOUCH_MEASUREMENT_PERIOD_MS	uint16_t	millisecond	Should be found through GPIO pin toggle procedure.	65535	20

PTC Interrupt Priority Level

The Nested Vectored Interrupt Controller (NVIC) in the SAM has four different priority levels. The priority level of the PTC end of conversion ISR can be selected based on application requirements to accommodate time critical operations. Setting the PTC interrupt priority level to lowest can have an impact on the touch response time, depending on the execution time taken by other higher priority interrupts.

Setting Configuration Name Data Type Unit Min Max Typical
PTC interrupt priority level	DEF_TOUCH_PTC_ISR_LVL	uint8_t	None	0 (Highest Priority)	3 (Lowest Priority)	3

To avoid stack overflow, ensure that adequate stack size has been set in the user application. This configuration is applicable only for SAM devices.

touch\_suspend\_app\_cb

Callback function pointer that must be initialized by the application before a touch library API is called. Touch library would call the function pointed by this function when suspension operation has to be carry on by the application.

Setting Configuration Name Data Type Returns
Suspend Callback	touch_suspend_app_cb	void(* volatile touch_suspend_app_cb) (void)	void

Low power Sensor Event Periodicity

When the CPU returns to standby mode from active, the sensor configured as the low power sensor is scanned at this interval. A high value for this parameter will reduce power consumption but increase response time for a low power sensor.

The following macros are used for configuring the low power sensor event periodicity:

• The macro LOWPOWER_PERO_SCAN_3_P_9_MS sets the scan rate at 3.9ms
  • The macro LOWPOWER PER1 SCAN 7 P 8 MS sets the scan rate at 7.8ms
  • The macro LOWPOWER PER2 SCAN 15 P 625 MS sets the scan rate at 15.625ms
  • The macro LOWPOWER PER3 SCAN 31 P 25 MS sets the scan rate at 31.25ms
• The macro LOWPOWER_PER4_SCAN_62_P_5_MS sets the scan rate at 62.5ms
  • The macro LOWPOWER PER5 SCAN 125 MS sets the scan rate at 125ms
• The macro LOWPOWER_PER6_SCAN_250_MS sets the scan rate at 250ms
• The macro LOWPOWER_PER7_SCAN_500_MS sets the scan rate at 500ms

Low power Sensor Drift Periodicity

This parameter configures the scan interval for a single active measurement during low power mode. This active measurement is required for reference tracking of low power sensor.

Setting	Configuration Name Data Type Unit Min Max Typical
Low power sensor drift rate	DEF_LOWPOWER_SENSOR_DRIFT_PERIODICITY_MS	uint16_t	milliseconds	0	65535	2000

Low power sensor ID

The macro DEF_LOWPOWER_SENSOR_ID is used to configure a sensor as low power sensor. Only one sensor can be configured as low power sensor. Low power sensor can be a normal sensor or a lumped sensor.

5.2.10. Moisture Parameters

Moisture Tolerance Enable

The macro DEF_XXXXCAP_MOIS_TOLERANCE_ENABLE is used to Enable or disable Moisture detection feature.

Moisture Quick Reburst

The macro DEF_XXXXCAP_MOIS_QUICK_REBURST_ENABLE is used to enable or disable quick re-burst feature within a given moisture group. When enabled, if within a given moisture group, when any sensor is touched, repeated measurements are done only that sensor to resolve detect integration or de-bounce. When disabled, if within a given moisture group, when any sensor is touched, repeated measurements are done on all sensors within the moisture group to resolve detect integration or de-bounce. It is recommended to enable this feature for best touch response time.

Moisture groups

The macro DEF_XXXXCAP_NUM_MOIS_GROUPS specifies the total number of individual moisture group present the system.

5.2.11. PTC Lines Ground Feature

PTC GPIO State

The macro DEF_XXXXCAP_PTC_GPIO_STATE is used to set the unmeasured self/mutual capacitance PTC lines to Ground / Vcc in between PTC measurement cycle. Setting the PTC lines to GND_WHEN_NOT_MEASURED will set the state of the pin to low whenever the pin is unmeasured. Setting the PTC lines to PULLHIGH_WHEN_NOT_MEASURED will make the PTC lines to float in between sensor measurement in a measurement cycle. It is recommended to set GND_WHEN_NOT_MEASURED configuration to get low power.

5.3. Moisture Tolerance

Moisture tolerance check executes at the end of each measurement cycle and compares the sum of delta of all sensors in a moisture tolerance group against pre-configured threshold. If delta sum is greater than sensor moisture lock threshold and less than system moisture lock threshold, then the ON-state sensors within moisture tolerance group will be considered as moisture affected.

If delta sum is greater than system moisture lock threshold, all sensors within the moisture tolerance group will be considered as moisture affected. This condition is referred as moisture global lock out. The library will come out of the moisture global lock out state when delta sum is less than threshold for 5 consecutive measurements. Self cap and mutual cap sensors cannot be configured in a single moisture group, Self cap moisture tolerance and mutual cap Moisture tolerance features can be enabled or disabled separately.

Note: Lumped sensor and the sensor which is part of the specific lump should not be assigned to same moisture group.

Figure 5-11. Moisture Tolerance Algorithm

graph TD
    A["START"] --> B["Start Process for first moisture group"]
    B --> C["Calculate delta sum of all Sensors configured in the moisture group"]
    C --> D{Any sensor is in detect?}
    D -->|No| E["Find the first sensor in the group in ON state and subtract it's delta from delta sum"]
    D -->|Yes| F{Any multi touch group in detect?}
    F -->|No| E
    F -->|Yes| G["Calculate multi touch group delta and Subtract from delta sum"]
    G --> E
    E --> H{Is delta sum > Sensor moisture lock threshold}
    H -->|No| I["Set moisture detect status of the sensors that are in detect"]
    H -->|Yes| J{Is moisture global Lock out is set?}
    J -->|No| K["Set next Moisture group"]
    J -->|Yes| L["Decrement lock count"]
    L --> M{Is Lock count zero?}
    M -->|No| N["Set moisture detect status of the sensors that are in detect"]
    M -->|Yes| O["Reset! All sensors moisture status bits"]
    O --> P["End"]
    N --> Q{Is this the Last moisture group?}
    Q -->|No| R["Set next Moisture group"]
    Q -->|Yes| S["End"]

5.3.1. Moisture Tolerance Group

This feature enables the customer application to group a set of sensors in to single moisture tolerance group. If moisture on one sensor might affect other sensors due to physical proximity, they must be grouped together into one Moisture tolerance group.

Using this feature the application can disable moisture tolerance detection for a set of sensors, Multiple Moisture tolerance groups can be formed by the customer application. The library supports up to a maximum of 8 moisture groups.

Note: Changing the moisture tolerance group configuration during runtime is not recommended. However, muti-touch group configuration can be changed during runtime.

5.3.2. Multi-touch Group

If the user wants to touch multiple sensors within the moisture tolerance group simultaneously to indicate a specificrequest, then the application should configure those sensors into single multi-touch group. Multiple multi-touch groups can be formed by the customer application. The library supports a maximum of 8 multi-touch groups within a single moisture tolerance group.

Moisture tolerance feature improves a system's performance under the following scenarios:

• Droplets of water sprayed on the front panel surface
  • Heavy water poured on the front panel surface
  • Large water puddle on multiple sensors

- Trickling water on multiple sensors

Moisture tolerance feature is not expected to offer any significant performance improvement under the following scenarios:

• Large isolated puddle on single sensor
- Direct water pour on single sensor

Within the same moisture group, user should not configure all the sensors to the single multi-touch group.

5.4. Reading Sensor States

When noise immunity and moisture tolerance features are enabled the validity of the sensor sate is based on the moisture status and noise status. Refer Noise Counter Measures and Moisture Parameters for information on noise immunity and moisture tolerance status of sensors. The state of a sensor is valid only when the sensor is not affected by noise and moisture. If a sensor is noisy or affected by moisture, then the state of sensor must be considered as OFF. The code snippet below depicts the same for mutual-cap sensors.

When a sensor is touched or released during DI, library will burst on channels corresponding to sensors whose state is other than OFF or DISABLED. If any sensor in an AKS group is in a state other than OFF or DISABLED, the library will burst channels corresponding sensors belong to that AKS group. If a sensor in any moisture group is in a state other than OFF or DISABLED, the library will burst on channels corresponding to sensors belonging to that moisture group.

if(! (GET_MUTLCAP_SENSOR_NOISE_STATUS(SENSOR_NUMBER)))
{
    if(! (GET_MUTLCAP_SENSOR_MOIS_STATUS (SENSOR_NUMBER)))
    {
    /*Sensor state is valid Read sensor state */
    }
    else
    {
    /* Sensor is Moisture affected*/
    }
}
else
{
    /* Sensor is noisy */
} 

5.5. Application Flow

5.5.1. Application Flow SAM

The application periodically initiates a touch measurement on either mutual capacitance or self-capacitance sensors. At the end of each sensor measurement, the PTC module generates an end of conversion (EOC) interrupt. The touch measurement is performed sequentially until all the sensors are measured. Additional post-processing is performed on the measured sensor data to determine touch status and rotor/slider position. An interrupt callback function is triggered to indicate completion of measurement. The recommended sequence of operation facilitates the CPU to either sleep or perform other functions during touch sensor measurement.

Before using the PTC, the generic clock generator for the PTC peripheral should be set up by the Application. It is recommended to set the PTC generic clock to 4MHz.

Figure 5-12. Application vs QTouch Library Flow

graph TD
    A["Initialize"] --> B["Time to measure touch?"]
    B --> C["Check touch status"]
    C --> D["Other functions"]
    D --> E["Sleep"]
    F["Enable EOC ISR"] --> G["Start Acquire Channel 0"]
    H["Store Result"] --> I["Last Channel Complete?"]
    I --> J["Sensor post-processing"]
    I --> K["Start Next Channel"]
    J --> L["Callback"]

5.5.2. Application Flow - megaAVR

The application periodically initiates a touch measurement on either mutual capacitance or self-capacitance sensors either in polled or interrupt mode. In polling mode, touch API's are blocking API's and will consume more CPU time. In ISR mode, touch API's are non blocking and will generate an end of conversion (EOC) interrupt at the end of each sensor measurement. Touch measurement is initiated on first sensor by calling touch_xxxxcap_sensors_measure() API. The touch measurement is initiated sequentially and additional post-processing is performed on the measured sensor data to determine touch status and rotor/slider position by calling touch_ptc_process() API in application context instead of interrupt context. A callback function is triggered to indicate completion of measurement. The ISR mode sequence of operation facilitates the CPU to either sleep or perform other functions during touch sensor measurement.

It is recommended to set the PTC clock to 4MHz.

Figure 5-13. Application vs QTouch Library Flow

graph TD
    A["Initialize"] --> B{If time to measure}
    B -->|No| C["Call touch_ptc_process"]
    B -->|Yes| D["Enable EOC ISR"]
    D --> E["Start Acquire Channel 0"]
    C --> F["Check touch status"]
    F --> G["Other functions"]
    G --> H["Sleep"]
    I["Is EOC done"] -->|No| J["Store Result"]
    I -->|Yes| K["Last Channel Complete?"]
    J --> L["Sensor post-processing"]
    J --> M["Start Next Channel"]
    L --> N["Callback"]
    M --> N

5.6. API Sequence

The touch_xx_sensors_init API initializes the QTouch Library as well as the PTC module. It also initializes the mutual or self-capacitance method specific pin, register, and global sensor configuration.

The touch_xx_sensor_config API configures the individual sensor. The sensor specific configuration parameters can be provided as input arguments to this API.

The touch_xx_sensors_calibrate API calibrates all the configured sensors and prepares the sensors for normal operation. The touch_xx_sensors_measure API initiates a sensor measurement on all the configured sensors.

Figure 5-14. API Sequence with Combined self and Mutual Capacitance Sensors Enabled

graph TD
    A["touch_xxxx cap_sensors_init"] --> B["configure multiple Touch sensors"]
    B --> C["touch_xxxx cap_sensors_config0"]
    C --> D["touch_xxxx cap_sensors_calibrate0"]
    D --> E["touch_xxxx cap_sensors_measure(NO RMAL_ACQ_MODE)"]
    E --> F["HostApplication code/SLEEP"]
    F --> G{Is Calibration completed?}
    G -->|No| H["time_to_measure_touch"]
    H --> I["touch_xxxx cap_sensors_measure(NO RMAL_ACQ_MODE)"]
    I --> J["PTC ISR (Normal measurement)"]
    J --> K["filter_callback(), if enabled"]
    K --> L["measure_complete_callback(), measured data and Touch Status"]
    L --> M["PTC ISR (Sensors Calibration)"]
    M --> N["measure_complete_callback(), measured data and Touch Status"]
    N --> O["Hold Application code/SLEEP"]
    O --> P["Call In loop"]

5.7. State Machine

The PTC QTouch Library state machine that presents the various library States and Event transitions can be found in the figure below. The state machine is maintained separately for each of the touch acquisition method, which means the state of mutual capacitance sensor operation can be different from the state of self-capacitance allowing them to co-exist.

Figure 5-15. Library State Machine

graph TD
    A["touch_xx_sensor_init"] --> B["touch_STATE_INIT"]
    B --> C["touch_xx_sensors_calibrate"]
    C --> D["touch_STATE_READY"]
    D --> E["touch_xx_sensors_measure"]
    E --> F["touch_STATE_BUSY"]
    F --> G["touch_xx_sensors_deinit"]
    G --> H["touch_STATE_NULL"]
    H --> I["touch_xx_sensors_init"]
    I --> J["touch_xx_sensor_config"]
    J --> K["touch_xx_sensor_get_config"]
    K --> L["touch_xx_sensor_get-config"]
    L --> M["touch_xx_sensor_get_global_param"]
    M --> N["touch_xx_sensor_get_acq_config"]
    N --> O["touch_xx_sensor_get_libinfo"]
    O --> P["touch_xx_sensor_init"]
    P --> Q["touch_xx_sensor Null"]
    Q --> R["touch_xx_sensors_deinit"]
    R --> S["touch_xx_sensors_deinit"]
    S --> T["touch_xx_sensors_deinit"]
    T --> U["touch_xx_sensors_meability"]
    U --> V["touch_xx_sensor_update_config"]
    V --> W["touch_xx_sensor_update_config"]
    W --> X["touch_xx_sensor_get_config"]
    X --> Y["touch_xx_update_global_param"]
    Y --> Z["touch_xx_sensor_get_global_param"]
    Z --> AA["touch_xx_sensor_update_acq_config"]
    AA --> AB["touch_xx_sensor_get_acq_config"]
    AB --> AC["touch_xx_sensor_disable"]
    AC --> AD["touch_xx_sensor_reenable"]
    AD --> AE["touch_xx_sensor_reenable"]
    AE --> AF["touch_xx_get_libinfo"]
    AF --> AG["touch_xx_get_libinfo"]
    AG --> AH["touch_suspend_ptc"]
    AH --> AI["touch_resume_ptc"]
    AI --> AJ["measure_complete_callback (provide measured data and touch status)"]
    AJ --> AK["measure_complete_callback (provide measured data and touch status)"]

The touch_xx_sensors_init API initializes the QTouch Library as well as the PTC module. It also initializes the mutual or self-capacitance method specific pin, register, and global sensor configuration.

The touch_xx_sensor_config API configures the individual sensor. The sensor specific configuration parameters can be provided as input arguments to this API.

The touch_xx_sensors_calibrate API calibrates all the configured sensors and prepares the sensors for normal operation.

The touch_xx_sensors_measure API initiates a sensor measurement on all the configured sensors.

The touch_xx_sensors_deinit function is used to clear the initialized library state. Used for clearing the internal library data and states. When called will modify the library state to TOUCH_STATE_NULL.

The touch_xxxx_lowpower_sensor_enable_event_measure API is used to start a event trigger based low power sensor measurement.

Touch Library Suspend Resume Operation

The touch library provides touch_suspend_ptc, touch_resume_ptc API to suspend and resume the PTC.

When suspend API is called, the touch library initiates the suspend operation and return to the application. After completing the current PTC conversion, the touch library will initiate suspend operation and call the application touch suspend callback function pointer. The suspend complete callback function pointer has to be registered by the application.

Note: If it is not registered, then the suspend call will return TOUCH_INVALID_INPUT_PARAM.

The application then should disable corresponding clock to reduce the power consumption. The following flowchart depicts the suspend sequence.

Figure 5-16. Suspend Sequence

graph TD
    A["SUPENSION_START"] --> B["Touch_suspend_ptc()"]
    B --> C{Is Callback Received?}
    C -->|No| D["Wait for touch_suspend_callback if touch state is in TOUCH_STATE_BUSY or perform some other application code without calling any Touch_lib APIs"]
    C -->|Yes| E["disable PTC GCLK disable APBCMASK disable GCLK generator disable GCLK source"]
    E --> F["SUSPENSION_COMPLETE"]

If the touch state is not TOUCH_STATE_BUSY the user can disable the clock and proceed to complete the suspend routine.

To resume the operations, perform the following sequence:

Figure 5-17. Resume Sequence

graph TD
    A["RESUMPTION_START"] --> B["Re-enable GLCK source\nRe-enable GCLK generator\nRE-enable APBCMASK\nRe-enable PTC GCLK"]
    B --> C["Touch_resume_ptc()"]
    C --> D["RESUMPTION_COMPLETE"]

The SAM controllers may be configured to operate PTC touch sensing autonomously using the Event System. In this mode, a single sensor channel is designated as the 'Low Power' key and may be periodically measured for touch detection without any CPU action. The CPU may be held in STANDBY throughout the operation, minimizing power consumption.

The low power key may be a discrete electrode with one Y (Sense) line for self-capacitance or one X (Drive) plus one Y (Sense) for mutual capacitance, or it may be a combination of multiple Drive and/or Sense lines as a lumped mode sensor as described.

With this method, a fast response may be achieved even in large key-count applications while operating at an extremely low power level, drawing less than 10uA at 3.3V.

5.8. Operation Modes

The QTouch Library can operate in the following sensor measurement modes.

• Periodic measurement
• Continuous measurement

5.8.1. Periodic Measurement

In the periodic measurement mode, sensor measurement is initiated by the application through a periodic event such as timer interrupt. The periodic measurement mode scenario is when none of the sensors are touched. While a long measurement period can be used to achieve lower device power consumption, a short measurement period is required for better touch response time. Hence, the measurement period should be tuned to suit a given application. Typical measurement period can range between 20 millisecond to 250 millisecond.

Figure 5-18. Periodic Measurement Mode

graph TD
    A["Application"] --> B["Initialize"]
    B --> C{Time to measure?}
    C -->|touch_xx_sensors_measure| D["Set Up Touch Measurement"]
    D --> E["API return"]
    E --> F["Start Mth Measurement Cycle"]
    F --> G["Acquisition on 1st channel"]
    G --> H["Acquisition on 2nd channel"]
    H --> I["Acquisition Complete on Last Channel ?"]
    I --> J["Sensor post-processing"]
    J --> K["Start( M+1) Measurement Cycle"]
    K --> L["Other Application functionality"]
    L --> M["Sleep"]
    M --> N{Is measurement? Yes complete?}
    N -->|touch_xx_measure_complete_callback| O["Perform touch actions"]
    O --> P["Perfor m touch actions"]
    P --> Q["touch_xx_measure_complete_callback"]
    Q --> R["Start( M+2) Measurement Cycle"]
    R --> S["Repetition measurements until the touch is resolved or Noise is removed"]

    T["CPU Time used by interrupt context"] --> U["PTC Time"]
    U --> V["End"]

5.8.2. Continuous Measurement

In the continuous measurement mode, back to back sensor measurement can be initiated from the touch library. This mode can be triggered to resolve user presence or resolve calibration under the following scenario.

• Resolve user presence, when sensor is touched or released

• Resolve calibration, when

• Sensor is calibrated using the touch_xx_sensors_calibrate API
  – Sensor is in Away from touch re-calibration condition

• Sensor is in Max-on duration condition

The TOUCH_BURST_AGAIN acquisition status data bit field in the measure data structure is set to indicate continuous measurement mode.

void touch_mutlcap_measure_complete_callback(void)
{
    if (!(p_mutlcap_measure_data->acq_status & TOUCH_BURST_AGAIN))
    {
    /* Set the Mutual Cap measurement done flag. */
    p_mutlcap_measure_data->measurement_done_touch = lu;
    }
} 

Touch Library Acquisition Status Flags

The touch library acquisition status information during continuous measurement mode is available using the touch_acq_status_t acq_status element of the touch_measure_data_t touch measure data structure.

Table 5-1. Touch Acquisition Status Bit Fields

Macro Bitfield Comment
TOUCH_NO_ACTIVITY	0x0000u	No Touch activity
TOUCH_IN_DETECT	0x0001u	Atleast one Touch channel is in detect
TOUCH_STATUS_CHANGE	0x0002u	Change in Touch status of atleast one Touch channel
TOUCH_ROTOR_SLIDER_POS_CHANGE	0x0004u	Change in Rotor or Slider position of atleast one rotor or slider
TOUCH_CHANNEL_REF_CHANGE	0x0008u	Change in Reference value of atleast one Touch channel
TOUCH_BURST_AGAIN	0x0008u	Indicates that reburst is required to resolve Filtering or Calibration state
TOUCH_RESOLVE_CAL	0x0200u	Indicates that reburst is needed to resolve Calibration
TOUCH_RESOLVE_FILTERIN	0x0200u	Indicates that reburst is needed to resolve Filtering
TOUCH_RESOLVE_DI	0x0800u	Indicates that reburst is needed to resolve Detect Integration
TOUCH_RESOLVE_POS_RECAL	0x1000u	Indicates that reburst is needed to resolve Recalibration
TOUCH_CC_CALIB_ERROR	0x2000u	Indicates that CC calibration failed on at least one channel
TOUCH_AUTO_OS_IN_PROGRES_S	0x4000u	Indicates that Auto OS in progress to get stable channel signal

The acquisition status flags can be monitored within the measure complete callback as shown.

void touch_mutlcap_measure_complete_callback(void)
{
    if ((p_mutlcap_measure_data->acq_status & TOUCH_BURST_AGAIN))
    {
    //Denotes acquisition is incomplete.
    }
    if ((p_mutlcap_measure_data->acq_status & TOUCH_RESOLUTION_CAL))
    {
    //Denotes sensor calibration is on-going.
    }
    if (!(p_mutlcap_measure_data->acq_status & TOUCH_BURST_AGAIN))
    {
    //Denotes acquisition is completed.
    /* Set the Mutual Cap measurement done flag. */
    p_mutlcap_measure_data->measurement_done_touch = lu;
    }
} 

Continuous Measurement Post Processing Mode

The sensor data post-processing mode for QTouch library can be selected using the DEF_xxxxCAP_TOUCH_POSTPROCESS_MODE configuration item available as part of touch.h file.

When TOUCH_LIBRARY_DRIVEN mode is selected, the library self-initiates repeated touch measurements to resolve touch press, release and calibration. This mode is suited for best response time.

When TOUCH_APPLN_DRIVEN mode is selected, the library does not initiate repeated touch measurement to resolve touch press, release and calibration. This mode suits deterministic PTC interrupt execution time for applications requiring stringent CPU time requirements. As repeated touch measurements are delayed due to other critical application code being executed. This mode can potentially affect the touch response time.

In order to improve the response time with the TOUCH_APPLN_DRIVEN mode, the following condition should be applied to initiate sensor measurement, so as to cater for additional measurements without any delay. The same condition can also be applied to other application scenario such as sleep to check for pending acquisitions to be completed before the system can go to sleep.

if ((touch_time.time_to_measure_touch == lu) || (p_mutlcap_measure_data->acq_status & TOUCH_BURST_AGAIN))
{
    /* Start a touch sensors measurement process periodically, or if there is a pending measurement. */
    touch_ret =
    touch_mutlcap_sensors_measure(touch_time.current_time_ms, NORMAL_ACQ_MODE, touch_mutlcap_measure_complete_callback);
} 

5.9. Touch Library API Error

The following table provides the touch library API error code information. The API error code type is touch_ret_t enum.

ErrorCode Enumeration Comment
TOUCH_SUCCESS	Successful completion of operation
TOUCH_ACQ_INCOMPLETE	Touch Library is busy with pending previous touch measurement
TOUCH_INVALID_INPUT_PARAM	Invalid input parameter
TOUCH_INVALID_LIB_STATE	Operation not allowed in the current Touch Library state
TOUCH_INVALID_SELFCAP_CONFIG_PARAM	Invalid self-capacitance configuration input parameter
TOUCH_INVALID_MUTLCAP_CONFIG_PARAM	Invalid mutual capacitance configuration input parameter
TOUCH_INVALID_RECAL_THRESHOLD	Invalid Recalibration threshold input value
TOUCH_INVALID_CHANNEL_NUM	Channel number parameter exceeded total number of channels configured
TOUCH_INVALID_SENSOR_TYPE	Invalid sensor type. Sensor type can not be SENSOR_TYPE_UNASSIGNED
TOUCH_INVALID_SENSOR_ID	Invalid sensor number parameter
TOUCH_INVALID_RS_NUM	Number of Rotor/Sliders set as 0, when trying to configure a rotor/slider

The application error codes in touch projects can be enabled or disabled using a macro DEF_TOUCH_APP_ERR_HANDLER. By default, the value of macro DEF_TOUCH_APP_ERR_HANDLER is set to 0 in order to disable the application error handler. To enable the application error handler, set the macro DEF_TOUCH_APP_ERR_HANDLER as 1. When it is enabled, while(1) is used to trap errors.

Refer Application Error Code (tag_touch_app_err_t) for further information.

6. Tuning for Noise Performance

The PTC has been designed with great care making it easy to design a capacitive touch solution, while at the same time maintaining high quality of touch and performance. Nevertheless in any touch sensing application, the system designer must consider how electrical interference in the target environment may affect the performance of the sensors.

Touch sensors with insufficient tuning can show failures in tests of either radiated or conducted noise, which can occur in the environment or power domain of the appliance or may be generated by the appliance itself during normal operation. In many applications there are quality standards which must be met where EMC performance criteria are clearly defined. However meeting the standards cannot be considered as proof that the system will never show EMC problems, as the standards include only the most commonly occurring types and sources of noise.

Noise immunity comes at a cost of increased touch response time and power consumption. The system designer must carry out proper tuning of the touch sensors in order to ensure least power consumption. The PTC QTouch library has anumber of user configurable features which can be tuned to give the best balance between touch response time, noise immunity and power consumption.

6.1. Noise Sources

Noise sources that affect touch sensor performance can be classified as follows.

Self-generated

• Motors
• Piezo buzzers
• PWM controls Radiated
• Fluorescent lamp
• Radio transmission
• Inductive cook top Conducted
  • Power supply / charger
• Mains supply

Applicable EMC standards

• Conducted Immunity EN61000-4-6

6.2. Noise Counter Measures

The effects of noise are highly dependent on the amplitude of the noise signal induced or injected onto the sensors, and the frequency profile of that noise signal.

Generally, this noise can be classified as -

• Broadband noise
• Narrow band noise

6.2.1. Broadband Noise Counter Measures

Broadband noise refers to noise signals whose frequency components are not harmonically related to the capacitance measurement acquisition frequencies of the PTC.

Provided that the maximum and minimum voltage levels of the acquisition signal combined with noise signals are within the input range of the PTC and a sufficiently large number of samples are taken,

broadband noise interference can be averaged out by setting a high value of Filter level

(DEF_MUTLCAP_FILTER_LEVEL_PER_NODE, DEF_SELFCAP_FILTER_LEVEL_PER_NODE) and Auto oversample (DEF_MUTLCAP_AUTO_OS_PER_NODE, DEF_SELFCAP_AUTO_OS_PER_NODE) settings.

If the noise amplitude is excessive, then PTC components experience saturation of measurement. In this case the acquisition signals combined with the noise signals are outside the input range of the PTC, which results in clipping of the measurements.

Often the clipping is not observable in the resolved measurement, as it occurs only on a portion of the measurement samples, but the presence of clipped samples prevents effective averaging of the sample points.

In this case, averaging of samples will not result in a noise-free measurement even with large rates of oversampling. The resolved signal will show a shift from its correct level due to asymmetry of signal clipping.

Configuration Parameter Setting
DEF_MUTLCAP_FILTER_LEVEL_PER_NODE,DEF_SELFCAP_FILTER_LEVEL_PER_NODE	FILTER_LEVEL_64
DEF_MUTLCAP_AUTO_OS_PER_NODE, DEF_SELFCAP_AUTO_OS_PER_NODE AUTO_OS_DISABLE
DEF_MUTLCAP_FREQ_MODE, DEF_SELFCAP_FREQ_MODE FREQ_MODE_NONE
DEF_MUTLCAP_CLK_PRESCALE_PER_NODE,DEF_SELFCAP_CLK_PRESCALE_PER_NODE	PRSC_DIV_SEL_1
DEF_MUTLCAP_SENSE_RESISTOR_PER_NODE,DEF_SELFCAP_SENSE_RESISTOR_PER_NODE	RSEL_VAL_100
Auto-tune input to touch_mutlcap_sensors_calibrate(),touch_selfcap_sensors_calibrate API	AUTO_TUNE_PRSC

STEP 1: PREVENT CLIPPING

This requires the implementation of a hardware low pass filter in order to reduce the scale of the noise combined with acquisition signal. The sensor capacitance is combined with a series resistor on the Y (Sense) line, either the PTC internal resistor or externally mounted on the PCB. The external series resistor should be mounted between the Y line of the device to the Sensor, closest to the device pin.

Note: Always use an external series resistor for self-capacitance applications in order to prevent clipping. The internal series resistor of the PTC is limited to 100K. Depending on the noise levels, external series resistors up to 1 megaohms can be evaluated.

STEP 2: CHARGE TRANSFER TEST

As an effect of adding a series resistor to form a low pass filter, the time constant for charging the sensors is increased. It is essential to ensure that the sensor capacitance is fully charged and discharged during each measurement sampling.

Insufficient charging can be observed as a reduced touch delta or it may be seen on an oscilloscope by connecting to the sense electrode.

However, this problem may not be apparent in the touch sensor operation; the application may behave perfectly well even in the presence of low-level noise, but show much worse performance during noise tests with the addition of the resistor compared to a configuration which excludes the resistor.

Charge transfer though Auto tuning setting:

The QTouch library Auto tune setting provides a mechanism which carries out a charge transfer test on each enabled key and sets the prescalar to the fastest available setting ensuring full charge transfer.

The following combination of setting should be used.

• DEF_MUTLCAP_SENSE_RESISTOR_PER_NODE and DEF_SELFCAP_SENSE_RESISTOR_PER_NODE should be set to RSEL_VAL_100.
• Auto tune pre-scaler AUTO_TUNE_PRSC should be provided as input parameter to touch_mutlcap_sensors_calibrate(AUTO_TUNE_PRSC) and touch_mutlcap_sensors_calibrate(AUTO_TUNE_PRSC)

Testing for Charge transfer by Manual tuning:

• If the AUTO_TUNE_NONE setting is provided as an input to the touch_mutlcap_sensors_calibrate(AUTO_TUNE_NONE) and touch_mutlcap_sensors_calibrate (AUTO_TUNE_NONE) calibration API, then the PTC uses the user defined settings of the PTC Clock pre-scaler (DEF_MUTLCAP_CLK_PRESCALE, DEF_SELFCAP_CLK_PRESCALE_PER_NODE) and internal series resistor (DEF_MUTLCAP_SENSE_RESISTOR_PER_NODE, DEF_SELFCAP_SENSE_RESISTOR_PER_NODE).
• Reference measurement: An acquisition measurement (Signal value) is taken with the prescalar set to maximum, i.e. PRSC_DIV_SEL_8

Test measurement: A second measurement (Signal value) is taken with reduced prescalar: PRSC_DIV_SEL_4

If the difference between the two measurements is less than 3% (1/32) of the first value, the conclusion is that fullcharge transfer is achieved with PRSC_DIV_SEL_4.

This measurement is repeated for PRSC_DIV_SEL_2 and PRSC_DIV_SEL_1 to find the fastest PTC operating speed for which full charge transfer is achieved.

STEP 3: ADJUST OVERSAMPLING

Once clipping is prevented by hardware filtering and full charge transfer is ensured the next step is to find the best settings for Filter level (DEF_MUTLCAP_FILTER_LEVEL_PER_NODE, DEF_SELFCAP_FILTER_LEVEL_PER_NODE) and Auto over samples (DEF_MUTLCAP_AUTO_OS_PER_NODE, DEF_SELFCAP_AUTO_OS_PER_NODE).

Auto over samples feature provides the advantage that additional samples are only taken on a sensor which has shown a significant change. In the absence of such a change, the measurement cycle can be much shorter compared to applying (* AUTO_OS) as the oversampling rate on every measurement. Care should be taken when using AUTO_OS to ensure that it does not occur too frequently.

The measurement time for FILTER_LEVEL samples can be represented as:

A+ (B * FILTER_LEVEL)

Where A is the total time for PTC configuration and post-processing, and B is the oversampling period (the per sample measurement time)

When AUTO_OS is applied, this time is increased to:

A + (B * FILTER_LEVEL*(1 + AUTO_OS))

FILTER_LEVEL should be sufficiently large to ensure that AUTO_OS is only applied during the worst-case noise circumstances.

6.2.2. Narrowband Noise Counter Measures

If the noise includes a frequency component which is related to the PTC capacitance measurement acquisition frequency, then no amount of oversampling will average out the noise effects. Any batch of measurement samples taken with the same sampling frequency will result in a measurement offset. The actual offset resulting from each measurement depends on the relative phase of the noise component and the sampling frequency.

This effect is illustrated in the following diagram, where the noise is represented by a sine wave.

STEP 4: SELECT FREQUENCY MODE

Note: Step1, Step2 and Step3 provided in the previous section should be used in combination with this step in a system which has both broadband noise and narrow band noise. Default settings provided before STEP1 should be used as a starting point before starting noise tuning.

With FREQUENCY_MODE_NONE, a single acquisition frequency is used and samples are taken at the fastest rate possible with the given pre-scalar setting. This gives the best response time, and with sufficient oversampling excellent noise immunity at all noise frequencies which are not related to the sampling frequency.

However in the case where the noise is at (or close to) a frequency which is harmonically related to the sampling frequency then the noise issue becomes severe, as illustrated above.

This is particularly important in applications where a frequency sweep test is required, such as EN61000-4-6.

FREQUENCY_MODE_SPREAD applies a modification to the sampling rate, such that the period between successivesamples is modified in a saw-tooth fashion to apply a wider spectrum to the sampling frequency. The sampling frequency F0 is thus spread across the range (F0/2, F0). With relatively low noise amplitude, this can be effective atimproving performance with minimal cost in response time.

FREQUENCY_MODE_HOP utilizes 3 base frequencies and a median filter to avoid using measurements taken at unaffected frequency. The frequencies should be selected to minimize the set of crossover harmonics within the problemfrequency band.

Each of the 3 frequencies is used in sequence for each measurement cycle.i.e.

• Cycle 1: All sensors measured with Frequency 0
• Cycle 2: All sensors measured with Frequency 1
• Cycle 3: All sensors measured with Frequency 2
• Cycle 4: All sensors measured with Frequency 0
• Cycle 5: All sensors measured with Frequency 1

If Frequency 0 is related to the noise frequency, then the measurements taken with F0 will show high variation. Using a median filter, this ensures that the outlying measurements will be rejected.

In some applications, self-generated noise may be present which affects one or more of the default HOP frequencies. In such a case, the HOP frequencies should be changed to avoid this frequency.

Some noise frequencies can occur which are close to harmonics of two of the HOP frequencies, in which case thesystem must be tuned with higher settings of FILTER_LEVEL or AUTO_OS to provide enough samples to average the noise out of the measurement.

Determining PTC Acquisition Frequency

The PTC acquisition frequency is given by the following formula,

PTC Acquisition Frequency = (1/ PTC Acquisition Time)

The PTC acquisition time is given by the following formula,

PTC Acquisition Time = (Cycles per Acquisition + Hop Freq) * PTC IO Clock Period

Where, Cycles per Acquisition = Number of PTC clock cycles required for each acquisition. This is a fixed value of 15. Hop Freq = PTC acquisition frequency delay setting

This parameter is represented in the touch.h file by the symbols DEF_MUTLCAP_HOP_FREQS and DEF_SELFCAP_HOP_FREQS.

The PTC acquisition frequency is dependent on the Generic clock input to PTC and PTC clock pre-scaler setting. This delay setting inserts n PTC clock cycles between consecutive measurements on a given sensor, thereby changing the PTC acquisition frequency.

FREQ_HOP_SEL_1 setting inserts 0 PTC clock cycles between consecutive measurements. FREQ_HOP_SEL_16 setting inserts 15 PTC clock cycles.

Hence, higher delay setting will increase the total time taken for capacitance measurement on a given sensor as compared to a lower delay setting. A desired setting can be used to avoid noise around the same frequency as the acquisition frequency.

Range: FREQ_HOP_SEL_1 to FREQ_HOP_SEL_16

Three frequency hop delay settings need to be specified when assigning values to this parameter. Duration of each PTC clock period is given by the following formula,

Where,

CLKPTC = Generic clock input to the PTC

Refer touch_configure_ptc_clock() API in touch.c file for clock configuration.

Prescaler = PTC clock prescaler setting

This parameter is represented in the touch.h file by the symbols

DEF_MUTLCAP_CLK_PRESCALE_PER_NODE and DEF_SELFCAP_CLK_PRESCALE_PER_NODE.

Example: If Generic clock input to PTC = 4MHz, then:

• PRSC_DIV_SEL_1 sets PTC Clock to 4MHz
• PRSC_DIV_SEL 2 sets PTC Clock to 2MHz
• PRSC_DIV_SEL_4 sets PTC Clock to 1MHz
• PRSC_DIV_SEL_8 sets PTC Clock to 500KHz

Example:

When CLKPTC = 4MHz, Prescaler = PRSC_DIV_SEL_1, the PTC Acquisition Frequencies obtained are as follows,

Hop Freq PTC Acquisition Frequency(kHz)
FREQ_HOP_SEL_1	66.67
FREQ_HOP_SEL_2	62.50
FREQ_HOP_SEL_3	58.82
FREQ_HOP_SEL_4	55.56
FREQ_HOP_SEL_5	52.63
FREQ_HOP_SEL_6	50.00
FREQ_HOP_SEL_7	47.62
FREQ_HOP_SEL_8	45.45
FREQ_HOP_SEL_9	43.48
FREQ_HOP_SEL_10	41.67
FREQ_HOP_SEL_11	40.00
FREQ_HOP_SEL_12	38.46
FREQ_HOP_SEL_13	37.04
FREQ_HOP_SEL_14	35.71
FREQ_HOP_SEL_15	34.48
FREQ_HOP_SEL_16	33.33

Note: The acquisition frequencies may vary based on the tolerance of the clock source.

7. Application Design

7.1. Touch Library and Associated Files

The table below provides the mandatory files required to use the QTouch library. In order to add QTouch functionality into an existing user example project, these files and associated library based on the compiler should be added to the user project.

Table 7-1. Touch Library Files

File Description
touch_api_ptc.h	QTouch Library API header file, contains API and Data structure used to interface with the library
touch.h	QTouch library configuration header file
touch.c	A helper file to demonstrate QTouch library initialization and sensor configuration
libsamxxx_qtouch_iar.a or libsamxxx_qtouch_gcc.a	QTouch library compiled for IAR or GCC compiler that supports both self-capacitance and mutual capacitance sensors.

7.2. Code and Data Memory Considerations

The table below captures the typical code and data memory required for QTouch library. The typical memory requirements provided in the table are arrived considering only Regular API usage in the application. Usage of Helper API would consume additional code memory.

Each measurement method requires additional data memory from the application for storing the signals, references, sensor configuration information, and touch status. This data memory is provided by the application as 'data block' array. The size of this data block depends on the number of sensors configured. The PRIV_xx_DATA_BLK_SIZE macro in touch_api_ptc.h calculates the size of this data memory block.

Table 7-2. Mutual Capacitance Method

Series Code	Memory Keys Only	Data Memory Keys Only	Code Memory Keys with Rotor or Slider	Data Memory Keys with Rotor or Slider
libsamdlx-qtouch-gcc.a	9602 845 111	14 861
libsamdlx-qtouch-iar.a	9005 497 103	77 513
libsamd2x-qtouch-gcc.a	9222 841 107	34 857
libsamd2x-qtouch-iar.a	8881 497 102	54 513
libsaml21-qtouch-gcc.a	9282 841 107	94 857
libsaml21-qtouch-iar.a	9744 497 111	15 513
libsamdal-qtouch-gcc.a	9222 841 107	34 857
libsamdal-qtouch-iar.a	8881 497 10254 513
libsamc2x-qtouch-gcc.a	9752 841 11264 857
libsamc2x-qtouch-iar.a	9209 501 10567 517
libsamr21-qtouch-gcc.a	9246 841 10758 857
libsamr21-qtouch-iar.a	8905 497 10277 513
libsaml22-qtouch-gcc.a	9886 841 11078 857
libsaml22-qtouch-iar.a	9509 501 10981 517
libatmega328pb_qtouch_gcc.a	13338 503 15760 532
libMega328PB_qtouch.r90	10761 578 12391 607
libatmega324pb_qtouch_gcc.a	14082 482 16520 631
atmega324pb_qtouch_iar.r90	10646 441 12379 562

In case of ATmega328PB, for a single touch channel (mutual capacitance mode) without noise, moisture, auto-tune and qdebug features, RAM usage is 503 bytes. RAM usage gets increased by 36 bytes for each additional channel.

Table 7-3. Self-capacitance Method

Series Code	MemoryKeys Only	Data MemoryKeys Only	Code MemoryKeys with Rotor or Slider	Data MemoryKeys with Rotor or Slider
libsamdlx-qtouch-gcc.a	9576 841 10	884 849
libsamdlx-qtouch-iar.a	8952 497 10	216 505
libsamd2x-qtouch-gcc.a	9198 845 10	506 845
libsamd2x-qtouch-iar.a	8841 497 10	101 505
libsaml21-qtouch-gcc.a	9258 841 10	566 845
libsaml21-qtouch-iar.a	9806 497 11	070 505
libsamdal-qtouch-gcc.a	9198 845 10	506 845
libsamdal-qtouch-iar.a	8841 497 10	101 505
libsamc2x-qtouch-gcc.a	9716 841 11	024 845
libsamc2x-qtouch-iar.a	9148 501 10	400 509
libsamr21-qtouch-gcc.a	9542 841 10	850 845
libsamr21-qtouch-iar.a	8851 497 10	115 505
libsaml22-qtouch-gcc.a	9530 841 11	158 845
libsaml22-qtouch-iar.a	9410 501 10	733 509
libatmega328pb_qtouch_gcc.a	13274 500 15	260 519
libMega328PB_qtouch.r90	10705 594 12	041 613
libatmega324pb_qtouch_gcc.a	14026 478 16	024 593
libMega328PB_qtouch.r90	10596 437 12	329 558

In case of ATmega328PB, for a single touch channel (self-capacitance mode) without noise, moisture, auto-tune and qdebug features, RAM usage is 500 bytes. RAM usage gets increased by 32 bytes for each additional channel.

Note:

1. The total number of sensors supported by a specific device variant is limited by the number of XY-lines as well as code, data, and stack memory requirements.
2. To save the memory utilized for code and data, new lib-nano C library has been used for GCC example projects.

8. Example Applications

8.1. Atmel Board Example Projects

The GCC Xplained Pro example projects can be accessed through File>New Example Project menu option in Atmel Studio.

The IAR Xplained Pro example projects can be accessed through Atmel QTouch Library PTC Partpack.

The following example projects are available for Xplained Pro kits:

• SAM D20 Xplained Pro and QT1 Xplained Pro Mutual Capacitance example application
  • SAM D20 Xplained Pro and QT1 Xplained Pro Self Capacitance example application
• SAM D21 Xplained Pro and QT1 Xplained Pro Mutual Capacitance example application
• SAM D21 Xplained Pro and QT1 Xplained Pro Self Capacitance example application
• SAM D20 Xplained Pro and QT1 Xplained Pro Mutual Capacitance example application with Lump-Low Power configuration
• SAM D20 Xplained Pro and QT1 Xplained Pro Self Capacitance example application with Lump-Low Power configuration

• SAM D11 Xplained Pro Self Capacitance example application

- SAM D10 Xplained Mini Self Capacitance example application

- SAM D20 QTouch Robustness Demo Moisture Example Application (self + mutual)

• SAM C20 QTouch Robustness Demo Moisture Example Application

- SAM D20 Xplained Pro and QT3 Xplained Pro Mutual Capacitance example application with Lump-Low Power configuration

- SAM L21 Xplained Pro and QT3 Xplained Pro Mutual Capacitance example application with Lump-Low Power configuration

- SAM DA1 Xplained Pro and QT4 Xplained Pro Self Capacitance example application

- SAM C21 Xplained Pro and QT1 Xplained Pro Mutual Capacitance example application

- SAM C21 Xplained Pro and QT1 Xplained Pro Self Capacitance example application

- SAM C21 Xplained Pro Self Capacitance example application(on-board sensor)

- SAM C21 Xplained Pro and QT5 Xplained Pro Mutual Capacitance example application

- SAM L22 Xplained Pro and Touch Segment LCD Xplained Pro Mutual Capacitance example application

- ATmega328PB Xplained Mini Self Capacitance example application

- ATmega324PB Xplained Pro and QT5 Xplained Pro Mutual Capacitance example application

Note: For SAM L22, it is recommended to set the PTC Clock to 8MHz.

Clock Configuration Changes in Projects:

• For SAM C20/C21 RevB devices, DPLL is used as the main clock and OSC32K is used as reference clock for the DPLL clock source. For SAM C20/C21 RevC devices, OSC48MHz is used as the main clock. This is demonstrated in the example projects by using the same project for both SAM C20/C21 RevB and SAM C20/C21 RevC devices.
• The example projects which have DFLL as main clock source use scaled OSC8MHz/OSC16MHz clock as the reference input clock.

• SAM L22 example project configures DFLL for 16MHZ (performance level - PL2) and utilizes it as the main clock. This clock setting offers high performance.

• SAM L22 low power user board project configures DFLL for 8MHZ (performance level - PL0) and utilizes it as the main clock. This clock setting offers low power consumption.

• SAM L21/L22 low power example projects are configured in PL0 (Low power oriented mode) with Buck regulator as the main regulator in standby sleep mode. This is the best suitable configuration to achieve low power numbers.

The example projects make use of Xplained Pro boards and the extension kits for showcasing touch. Those extension kits are explained in the following sections.

QT1 Xplained Pro kit:

The QT1 Xplained Pro self-capacitance and mutual capacitance extension boards are supported by SAM D20, SAM D21, SAM DA1, SAM C21, and SAM L22 Xplained Pro Evaluation kits.

Figure 8-1. QT1 Xplained Pro Mutual Capacitance and Self-capacitance

STRAW NUTRAL CAPACITY RUMS BUTTON 1 BUTTON 2 Atme

MOTOR 5V CAPACITANCE SLABR MHEEL BUTTON 1 BUTTON 2 Atmel

Note: SAM C21 Xplained Pro can operate at 3.3V and 5V Vcc, while the QT1 Xplained Pro can operate at a maximum voltage of 3.6V. Please make sure to put the Vcc selection header on the SAM C21 Xplained Pro in the 3.3V position.

The QT1 Xplained Pro boards demonstrate the following combinations of buttons, slider, and wheels.

• 2 buttons + 2 yellow LED
  • 1 slider + 8 yellow LED
• 1 wheel + 1 RGB LED

QT3 Xplained Pro kit:

The QT3 Xplained Pro extension board has 12 mutual capacitance buttons on it and it is supported by SAM D20, SAM D21, SAM DA1, SAM L21, SAM L22 and SAM C21 Xplained Pro Evaluation kits.

Figure 8-2. QT3 Xplained Pro

QT3 X PLAINED PRO 1 2 3 4 5 6 7 8 9 C 0 # ATmet

QT4 Xplained Pro kit:

The QT4 Xplained Pro boards demonstrate the following arrangement.

• Two self-capacitance buttons
  • One unshielded proximity sensor
  • One proximity sensor with driven shield with external op-amp driver
  • One LED indicator for each self-capacitive button
  • One LED indicator for each proximity sensor

Figure 8-3. QT4 Xplained Pro

QTO X PLAINED RED QTOUCH SELF CAPACITANCE & PROXIMITY PROXIMITY - UNSHIELDED BUTTON 1 BUTTON 2 PROXIMITY - DRIVEN SHIELD Atmel

QT5 Xplained Pro kit:

The QT5 Xplained Pro board demonstrates the following arrangement.

• One 4-channel (4X x 1Y) mutual capacitance curved slider
- Two mutual capacitance buttons
• 16 LEDs arranged as two 7-segment digits separated with a colon
• IS31FL3728 I2C LED matrix controller from ISSI

Figure 8-4. QT5 Xplained Pro

Close-up of a circular electronic device with segmented components and a clock, no visible text or symbols.

8.2. User Board Example Projects

Atmel Studio QTouch Composer can be used to create GCC projects based on the sensor and pin configuration defined by the requirements of a user board. The generated example projects also allow for QDebug data streaming to QTouch Analyzer.

The User board example project can be generated by accessing the QTouch Composer using the following menu options in the Atmel Studio.

File > New Project > GCC C QTouch Executable Project > Create QTouch Library Project

The QTouch Project Builder wizard appears as shown in the screenshot. Selection of sensors, devices, pins, debug interface and tuning of parameters can be done according to user preferences and project can be generated. The figure shows one of the user board generated projects.

Figure 8-5. QTouch Project Builder

QTouch Project Builder Project Builder Workflow 1. Sensor Selection Button Slider Wheel 2. Device Selection 3. Pin Selection 4. Debug Interface Setup (optional) 5. BSW Channel Properties (optional) 6. Tuning Parameter Setup (optional) 7. Project Generation Please click on a sensor (in) drag and drop sensor shape to canvas to add sensors to layout

Figure 8-6. User Board Example Project

GetQTouchApplications3 - AtmaStudio (Administrator) File Edit View Microsoft ASP Project Build Debug Tools Window Help Debug Debug Debug Response <|vision_start|> main(void) { /** * Initialize and configure system and generic clocks. * This core _clock to configure system and generic clocks. * This example project was internal DPs oscillator. * The PTC module clock is provided using GPIO generator 1; */ system_init(); /** * Initialize delay service. */ delay_init(); /** * Initialize timer. * This example projects use RTC timer for providing timing * info to @touch library. */ timer_init(); /** * Initialize QTouch Library and configure touch sensors. */ touch_sensors_init(); /* config your system Sleep mode to standby MODE. */ system_set_110mode(SYSTEM_SLEEPMODE_STANDARD); while (1) { /** * Update STANDRY Sleep mode, unless chosen by timer or PTC "Interrupt. } }

8.3. Using Atmel Software Framework (ASF) with the Example Projects

The example projects are based on Atmel Software Framework (ASF). For more information on ASF refer to Atmel Software Framework User Guide http://www.atmel.com/.

The Atmel® Software Framework (ASF) is a MCU software library providing a large collection of embedded software for Atmel flash MCUs: mega AVR, AVR XMEGA, AVR UC3 and SAM devices.

• It simplifies the usage of microcontrollers, providing an abstraction to the hardware and high-value middleware
• ASF is designed to be used for evaluation, prototyping, design and production phases
  • ASF is integrated in the Atmel Studio IDE with a graphical user interface or available as standalone for GCC, IAR compilers
  • ASF can be downloaded for free

8.4. Using Xplained Pro Kit to Program User Board

The SAM D20 Xplained Pro features a Cortex® Debug Connector (10-pin) for programming and debugging an external target. The connector is limited to the SWD interface and is intended for in-system programming and debugging of SAM D20 devices in the final product developed by the users. For more information refer SAM D20 Xplained Pro User Guide (www.atmel.com).

8.5. Using QDebug Touch Data Debug Communication Interface

When using IAR and GCC example projects, QDebug touch data debug communication interface can be enabled. This allows the communication between the touch device and QTouch Analyzer.

To enable or disable QDebug, configure DEF_TOUCH_QDEBUG_ENABLE in the touch.h file.

When QDebug is enabled and touch debug data is being updated in the QTouch Analyzer, touch response time will be slower due to the debug communication data transfer which increases the delay in the response time.

After tuning the touch sensors using QTouch Analyzer, disable the QDebug for optimized touch performance.

Figure 8-7. Atmel DGI Interface for QDebug Data

QSO Analysis QSOAL-058 - 06444 Connect Start Reading Save Trace Open Trace File Save Design File Save Cart File No Kit Connected Help Graph View Estimate View Signal Selection Automatic Scale Marcus Scale Selection Default Camera View No Kit Connected IOI Settings Interface Character Length: 2000000 ISO Mask: Remplubified ISO Mask OK Cancel Max Max samples

Figure 8-8. QTouch Analyzer view

Touch Analyzer QD#RJAL D28 - 06444 Interconnect Size Based Map Save Trace Open Stream File Save Design File Save Case File The Solution Found Help Virtual Key View Graph View Table View Buttons Button Id Name State Delta Delta RM1 Channel Id Signal Reference 0 Button0 OFF 1 0 0 $15 $24 1 Button0 OFF 1 0 1 $12 $13 Wheels +/- Wheels Id Name State Delta Delta RM5 Position 0 Wheels0 OFF 2 0 0 Channel Id Signal Reference 2 SL2 SL1 3 SL3 SL3 4 SL2 SL3 Wlisters +/- Wlisters Id Name State Delta Delta RM6 Position 0 Shelset0 FMS SCL 0 ZB3 Channel Id Signal Reference 5 SL2 SL3 6 7M8 SL3 7 628 SL2 Connected

8.6. Using Xplained Pro Kit for QDebug Data Streaming from User Board

SAM D20 Xplained Pro contains Embedded Debugger (EDBG) that features an Atmel Data Gateway Interface (DGI) over SPI and TWI. The DGI can be used to transmit a variety of data from the Xplained Pro kit to the host PC. This arrangement can be used to send QDebug data from a user board to Atmel Studio QTouch Analyzer for touch sensor data analysis and tuning.

Figure 8-9. Using Xplained Pro for Data Streaming from User Board

graph LR
    A["QTouch Analyzer"] --> B["SAM B20 Xplanned Pro"]
    B --> C["Customer Board"]
    C --> D["QTEM"]
    C --> E["QRF"]
    C --> F["QTRF"]
    B --> G["USB"]
    G --> H["SAM E20"]
    H --> I["10"]
    I --> J["10"]
    J --> K["10"]
    K --> L["10"]
    L --> M["10"]
    M --> N["10"]
    N --> O["10"]

The example project generated using QTouch composer makes use of SPI for data transfer. To stream QDebug data from user board, a relay firmware should be flashed onto the SAM D20/D21 microcontroller on the Xplained Pro kit. After connecting the SAM D20/D21 Xplained Pro to the PC, the device name appears in the connected kits of QTouch Start Page. Right click the device name and choose Enable User Board Analysis to flash the relay firmware.

Figure 8-10. Flash Relay Firmware

QTouch Start Page - AtmelStudio (Administrator) File Edit View Insert ASF Project Debug Tools Window Help Enable User board Analysis (Not applicable for QT1 Xplained Pro int) Xplained Pro (Eg. SAM D20 Xplained Pro, SAM D21 Xplained Pro) contains Embedded Debugger (EDBG) that features an Atmel Data Gateway Interface (DGI) over SPI and TWL. The DGI can be used to send a variety of data from the Xplained Pro kit to the boat PC. This arrangement can be used to send QDebug data from a user board to QTouch Analyzer for touch sensor data analysis and tuning. The SAM device on the Xplained Pro is operated in SPI slave mode. User board analysis is only available in 3.3V (no level converters in place). Below figure illustrates connection between the SAM D20 Xplained Pro and customer board. To enable touch data streaming, flash the relay firmware into SAMO20 XPRO. QTouch Analyzer SAM D20 Xplained Pro Customer Board Flash Close Output Show output from Build Edit User Output

The following table indicates the SPI connection between SAM D20 Xplained Pro Kit and User Board:

Table 8-1. SPI Connection Information

SAMD20 Xplained Pro Extension header EXT3 UserBoard Pin
Pin on EXT3 Function
16 SPIMOSI (PB22) MOSI
17 SPIMISO (PB16) MISO
18 SPISCK(PB23) SCK
- SS-Connect to GND
19 GND GND

8.7. Using Atmel ICE for QDebug Data Streaming from User Board

Atmel ICE can be used to stream data from the user board.

Refer the following table and connect the mini squid cable from AVR header of Atmel ICE to user board.

Atmel-ICE AVR port pins Target pins Mini-squid pin
Pin 1 (TCK) SCK 1
Pin 2 (GND) GND 2
Pin 3 (TDO) MISO 3
Pin 4 (VTG) VCC 4
Pin 5 (TMS) SS 5
Pin 6 (nSRST) - 6
Pin 7 (Not Connected) - 7
Pin 8 (nTRST) - 8
Pin 9 (TDI)	MOSI 9
Pin 10 (GND)	- 0

While creating the project using QTouch composer project builder wizard, the pins SCK, MISO, SS and MOSI can be chosen from the debug interface setup pane as shown in the figure.

Figure 8-11. Debug Interface Setup Pane

QTouch Project Builder Project Builder Workflow 1. Sensor Selection 2. Device Selection - AISAMD11D14AM 3. Pin Selection - Done 4. Debug Interface Setup (optional) - Done A8 A9 A10 A11 A14 A15 A2 A3 A4 A5 A6 A7 A27 A28 A30 A31 Pin assigned for debug interface Available Pin PTC Pin assigned for sensor channel 5. BSW Channel Properties (optional) 6. Tuning Parameter Setup (optional) 7. Project Generation Command Enable QDebug Interface (QDebug interface allows Live streaming of Touch data to QTouch Analyzer) Debug Interface SW implemented S Name Y Pin SPI_BB_SS PA27 SPI_BB_SCK PA7 SPI_BB_MOSI PA6 SPI_BB_MISO PA9 Reset

When the connections are made correctly and debug interface setup is also done in the project, flash the project in the user board. Data can be streamed and visualized via QTouch Analyzer.

Note: Atmel ICE would be listed in QTouch Analyzer as QDEBUG_DGI.

9. Known Issues

1. PTC in Self-capacitance Mode

The following errata is applicable for SAM D20 (Revision B)

Description:

The two lowest gain settings are not selectable and an attempt by the QTouch Library to set enable of these may result in a higher sensitivity than optimal for the sensor. The PTC will not detect all touches. This errata does not affect mutual capacitance mode which operates as specified.

Fix/workaround:

Use SAM D20 revision C or later for self-capacitance capacitive touch sensing.

2. Touch acquisition may fail and stop working

The following errata is applicable for QTouch Library versions up to 5.0.7. This issue has been fixed in QTouch Library version 5.0.8 or later.

Description:

In QTouch applications, where either a single interrupt or a chain of nested non-PTC interrupts has duration longer than the total touch measurement time, the touch acquisition may fail and stop working. This issue occurs most likely in applications with few touch channels (2-3 channels) and a low level of noise handling (filter level 16 or lower and no frequency hopping).

In an application with single touch channel and filter level 16, the total measurement time is 350 s . The total measurement time doubles for two touch channels, and triples for 3 touch channels. It increases up to 10 times or 3.5ms with 10 touch channels.

Fix/workaround:

- Recommended workaround:

- Use QTouch Library version 5.0.8 or later.

- Other alternatives:

1. Always ensure that the duration of a single interrupt or a chain of nested non-PTC interrupts does not exceed the total touch measurement time. (or)
2. Add a critical section by disabling interrupts for the touch_xxxxcap_sensors_measure() function as shown in the following code snippet.

Disable_global_interrupt();
touch_ret = touch_xxxxcap_sensors_measure(touch_time.current_time_ms, NORMAL_ACQ_MODE, touch_xxxxcap_measure_complete_callback);
Enable_global_interrupt(); 

The Interrupt Blocking Time while executing touch_xxxxcap_sensors_measure API for various CPU frequencies are as follows.

CPU Frequency (in MHz) Interrupt Blocking Time ( in μs )
48 ~77
24 ~124
16 ~176
12 ~223

The interrupt blocking time varies based on the PTC_GCLK frequency, CPU frequency, and the library version. The actual blocking time can be measured by toggling a GPIO pin before and after the touch_xxxxcap_sensors_measure function.

When IAR compiler is used, utilize the system_interrupt_enable_global() and system_interrupt_disable_global() functions to enable and disable the global interrupts, respectively. In case of AVR, use cli() and sei() instructions to disable and enable the global interrupts.

10. FAQ on PTC Qtouch

Table 10-1. Frequently Asked Questions

Query Answer
When can we change an acquisition, sensor configuration or global sensor parameter?After changing an acquisition parameter do we need to recalibrate or reinitialize the sensors and PTC?	Its best to call the helper APIs to update these parameter when the measurement_done_touch flag (part oftouch_measure_data_t structure) is true, which means the library is not in the middle of an (previously started) incomplete acquisition. Changing Gain and Filter level settings can affect the Signal value, so recalibration is mandatory by invoking the touch_sensors_calibrate() API.
Can sensors be disabled and re-enabled run time?For example, scan 2 sensors while sleeping and then scan all sensors when the system wakes up.	Yes, this is possible using thetouch_xxxcap_sensor_disable() andtouch_xxxcap_sensor_reenable() API.
There is a low amplitude pulse prior to the 16 acquisition samples and a large amplitude pulse after the 16 acquisition samples.	These pulses are part of setting up the sense line's initial conditions.
Is Detect integration calculated inside the PTC or by QTouch library?	This is done by QTouch library.
When Auto Oversampling is enabled how can one determine touch timing?	The absolute maximum cycle, is the case that auto oversamples is applied to all channels: (Normal acquisition time) x (1 + auto_os).This can only happen with a poorly tuned system, as FILTER_LEVEL should be sufficient to prevent AUTO_OS happening except on a touched key under noisy conditions.
Can sensor signal lines (Y or X lines) be used to drive LEDs, etc., when not being used for sensor acquisitions?	No. This is not recommended

11. Appendix

11.1. Macros

11.1.1. Touch Library Acquisition Status Bit Fields

Keyword Type Description
TOUCH_NO_ACTIVITY	0x0000u	No touch activity.
TOUCH_IN_DETECT	0x0001u	Atleast one touch channel is in detect.
TOUCH_STATUS_CHANGE	0x0002u	Change in touch status of at least one Touch channel.
TOUCH_ROTOR_SLIDER_POS_CHANGE	0x0004u	Change in the position of at least one rotor or slider.
TOUCH_CHANNEL_REF_CHANGE	0x0008u	Changein the reference value of at least one touch channel.
TOUCH_BURST_AGAIN	0x0100u	Indicates that re-burst is required to resolve filtering or calibration state.
TOUCH_RESOLVE_CAL	0X0200u	Indicates that re-burst is required to resolve calibration.
TOUCH_RESOLVE_FILTERIN	0x0400u	Indicates that re-burst is required to resolve calibration.
TOUCH_RESOLVE_DI	0x0800u	Indicates that re-burst is needed to resolve Detect Integration.
TOUCH_RESOLVE_POS_RECAL	0x1000u	Indicates that re-burst is needed to resolve recalibration.
TOUCH_CC_CALIB_ERROR	0X2000u	Indicates that CC calibration failed on at least one channel.
TOUCH_AUTO_OS_IN_PROGRESS	0X4000u	Indicates that Auto-os in progress to get stable channel signal.

11.1.2. Sensor State Configurations

GET\_SENSOR\_STATE (SENSOR\_NUMBER)

To get the sensor state (whether detect or not) for parameter that corresponds to the sensor specified using the SENSOR_NUMBER.

The macro returns either 0 or 1. If the bit value is 0, the sensor is not in detect. If the bit value is 1, the sensor is in detect.

#define GET_XXXXCAP_SENSOR_STATE(SENSOR_NUMBER) p_xxxxcap_measure_data->p_sensor_states
[(SENSOR_NUMBER / 8)] & (1 << (SENSOR_NUMBER % 8))) >> (SENSOR_NUMBER %8) 

GET_XXXXCAP_SENSOR_MOIS_STATUS (SNSR_NUM)

To get the moisture status of a particular sensor. The return value is 1 in case of sensor is affected by moisture and returns 0 if sensor is affected by moisture.

#define GET_XXXXCAP_SENSOR_MOIS_STATUS(SNSR_NUM) ((p_xxxxcap_measure_data->p_sensor_mois_status
[(SNSR_NUM)/8] & (1<<((SNSR_NUM)%8))) >>(SNSR_NUM %8)) 

GET\_XXXXCAP\_MOIS\_GRP\_SUM\_DELTA (GRP\_ID)

To get the xxxcap moisture group sum delta.

The return value is 32 bit integer indicating the sum delta of moisture group.

#define GET_XXXXCAP_MOIS_GRP_SUM_DELTA(GRP_ID)(mois_XXXX_grp_delta_arr[(GRP_ID)-1]) 

GET\_XXXXCAP\_MOIS\_GRP\_ADJ\_DELTA (GRP\_ID)

To get the xxxcap moisture group Adjacent delta .The return value is 32 bit integer indicating the adjacent delta of moisture group.

#define GET_MUTLCAP_MOIS_GRP_ADJ_DELTA(GRP_ID)(mois_mut1_grp_adj_delta_arr[(GRP_ID)-1]) 

GET\_MOIS\_XXXX\_GLOB\_LOCK\_STATE

To get the moisture lock status of xxxcap moisture groups. The return value is 1 if any moisture group is in moisture global lockout and 0 if no moisture group is in moisture global lockout.

#define GET_MOIS_MUT_GLOB_LOCK_STATE(mois_lock_global_mutl) 

GET\_XXXXCAP\_SENSOR\_NOISE\_STATUS (SENSOR\_NUMBER)

To get the noise status of a particular sensor. The return value is 1 in case of sensor is noisy and returns 0 if sensor is not noisy.

#define GET_XXXXCAP_SENSOR_NOISE_STATUS (SENSOR_NUMBER)(p_xxxxcap_measure_data->p_sensor_noise_status
[(SENSOR_NUMBER / 8)] & (1 << (SENSOR_NUMBER % 8))) >> (SENSOR_NUMBER % 8) 

GET\_ROTOR\_SLIDER\_POSITION (ROTOR\_SLIDER\_NUMBER)

To get the rotor angle or slider position. These values are valid only when the sensor state for corresponding rotor or slider state is in detect.

ROTOR SLIDER NUMBER is the parameter for which the position is being obtained.

The macro returns rotor angle or sensor position.

#define
GET_XXXXCAP_ROTOR_SLIDER_POSITION(ROTOR_SLIDER_NUMBER)p_xxxxcap_measure_data->p_rotor_slider_values
[ROTOR_SLIDER_NUMBER] 

DEF_TOUCH_MUTLCAP must be set to 1 in the application to enable the Mutual capacitance touch acquisition method.

DEF_TOUCH_SELFCAP must be set to 1 in the application to enable the Self-capacitance touch acquisition method.

11.2. Typedef

Field Unit Description
threshold_t uint8_t		An unsigned 8-bit number setting a sensor detection threshold.
sensor_id_t uint8_t		Sensor number type.
touch_current_time_t uint16_t		Current time type.
touch_delta_t int16_t		Touch sensor delta value type.
touch_acq_status_t uint16_t		Status of touch measurement.
mois_snsr_threshold_t int32_t		Moisture threshold for individual sensor.
mois_system_threshold_t int32_t		Moisture threshold for the entire system.

11.3. Enumeration

11.3.1. Gain Setting (tag\_gain\_t)

Gain per touch channel.

Gain is applied on a per-channel basis to allow a scaling-up of the touch sensitivity on contact.

Range: GAIN_1 (no scaling) to GAIN_32 (scale-up by32)

Data Fields

GAIN_1
GAIN_2
GAIN_4
GAIN_8
GAIN_16
GAIN_32

11.3.2. Filter Level Setting (tag\_filter\_level\_t)

Touch library FILTER LEVEL setting.

The filter level setting controls the number of samples acquired to resolve each acquisition. A higher filter level setting provides improved signal to noise ratio under noisy conditions, while increasing the total time for measurement which results in increased power consumption. Refer filter_level_t in touch_api_ptc.h

Range: FILTER_LEVEL_1 (one sample) to FILTER_LEVEL_64 (64 samples).

Data Fields

FILTER_LEVEL_1
FILTER LEVEL 2
FILTER_LEVEL_4
FILTER_LEVEL_8
FILTER LEVEL 16
FILTER_LEVEL_32

FILTER_LEVEL_64 

11.3.3. Auto Oversample Setting (tag\_auto\_os\_t)

Auto oversample controls the automatic oversampling of sensor channels when unstable signals are detected with the default setting of 'Filter level'. Enabling Auto oversample results in 'Filter level' x 'Auto Oversample' number of samples taken on the corresponding sensor channel when an unstable signal is observed. In a case where 'Filter level' is set to FILTER_LEVEL_4 and 'Auto Oversample' is set to AUTO_OS_4, 4 oversamples are taken with stable signal values and 4+16 oversamples are taken when unstable signal is detected.

Range: AUTO_OS_DISABLE (oversample disabled) to AUTO_OS_128 (128 oversamples).

Data Fields

AUTO_OS_DISABLE
AUTO OS 2
AUTO_OS_4
AUTO_OS_8
AUTO OS 16
AUTO OS 32
AUTO OS 64
AUTO_OS_128

11.3.4. Low Power Sensor Scan Rate (tag\_lowpower\_scan\_int\_t)

When the CPU returns to standby mode from active, the sensor configured as the low power sensor is scanned at this interval. A high value for this parameter will reduce power consumption but increase response time for a low power sensor.

Note: This enum is applicable only for ATmega devices.

Range: LOWPOWER_PER0_SCAN_3_P_9_MS to LOWPOWER_PER7_SCAN_250_MS

Data Fields

• LOWPOWER_PER0_SCAN_3_P_9_MS
• LOWPOWER_PER1_SCAN_7_P_8_MS
• LOWPOWER_PER2_SCAN_15_P_625_MS
• LOWPOWER_PER3_SCAN_31_P_25_MS
• LOWPOWER_PER4_SCAN_62_P_5_MS
• LOWPOWER_PER5_SCAN_125_MS
• LOWPOWER_PER6_SCAN_250_MS

11.3.5. Library Error Code (tag\_touch\_ret\_t)

Touch Library error codes.

Data Fields

• TOUCH_SUCCESS Successful completion of touch operation.
  • TOUCH_ACQ_INCOMPLETE Library is busy with pending previous touch measurement.
• TOUCH_INVALID_INPUT_PARAM Invalid input parameter.
• TOUCH_INVALID_LIB_STATE Operation not allowed in the current touch library state.

• TOUCH_INVALID_SELFCAP_CONFIG_PARAM Invalid self-capacitance configuration input parameter.

• TOUCH_INVALID_MUTLCAP_CONFIG_PARAM Invalid mutual capacitance configuration input parameter.
  TOUCH_INVALID_RECAL_THRESHOLD Invalid recalibration threshold input value.

• TOUCH_INVALID_CHANNEL_NUM Channel number parameter exceeded total number of channels configured.
• TOUCH_INVALID_SENSOR_TYPE Invalid sensor type. Sensor type must NOT be SENSOR_TYPE_UNASSIGNED.
• TOUCH_INVALID_SENSOR_ID Invalid sensor number parameter.
• TOUCH_INVALID_RS_NUM Number of rotor/sliders set as 0, while trying to configure a rotor/slider.

11.3.6. Application Error Code (tag\_touch\_app\_err\_t)

The application error codes are listed below.

Data Fields

• TOUCH_INIT_CONFIG_ERR The touch_xxxxcap_sensors_init is fed with an incompatible / incomplete parameter.
• TOUCH_SENSOR_CONFIG_ERR The touch_xxxxcap_sensor_config is fed with an incompatible parameter / Touch Library state is not in TOUCH_STATE_INIT.
• TOUCH_INIT_CALIB_ERR The touch_xxxxcap_sensors_calibrate is fed with an invalid parameter / Touch Library state is TOUCH_STATE_NULL/ TOUCH_STATE_BUSY.
• TOUCH_MEASURE_INCOMPLETE The touch_measure api has error due to an invalid input param / it was on an invalid Touch Library state.
• TOUCH_MEASURE_CC_CAL_FAILED Hardware calibration error; check the hardware and ensure it is proper. If the error persists, check the user manual for sensor design guidelines.

11.3.7. Touch Channel (tag\_channel\_t)

Sensor start and end channel type of a Sensor. Channel number starts with value 0.

Data Fields

CHANNEL_0 to CHANNEL_255

11.3.8. Touch Library State (tag\_touch\_lib\_state\_t)

Touch library state.

Data Fields

• TOUCH_STATE_NULL Touch library is un-initialized. All sensors are disabled.
• TOUCH_STATE_INIT Touch library has been initialized
• TOUCH_STATE_READY Touch library is ready to start a new capacitance measurement on enabled sensors.
  TOUCH_STATE_CALIBRATE Touch library is performing calibration on all sensors.
  • TOUCH_STATE_BUSY Touch library is busy with on-going capacitance measurement.

11.3.9. Sensor Type (tag\_touch\_lib\_state\_t)

Sensor types available.

Data Fields

• SENSOR_TYPE_UNASSIGNED Sensor is not configured yet

• SENSOR_TYPE_KEY Sensor type key

• SENSOR_TYPE_ROTOR Sensor type rotor

• SENSOR_TYPE_LUMP Sensor type lump
• SENSOR_TYPE_SLIDER Sensor type slider
• MAX_SENSOR_TYPE Max value of enum type for testing

11.3.10. Touch Sensing Type (tag\_touch\_acq\_t)

Based on the two types of charge transfer technology, the capacitive touch sensing may be either mutual capacitance sensing or self-capacitance sensing.

Data Fields

• TOUCH MUTUAL Mutual capacitance sensing
  • TOUCH_SELF Self-capacitance sensing
  • MAX_TOUCH_ACQ Max value of enum

11.3.11. Touch Library Acquisition Mode (tag\_touch\_acq\_mode\_t)

Touch library acquisition mode.

Data Fields

RAW\_ACQ\_MODE

When raw acquisition mode is used, the measure_complete_callback function is called immediately once a fresh value of signals are available. In this mode, the Touch Library does not perform any post processing. So, the references, sensor states or rotor/slider position values are not updated in this mode.

NORMAL\_ACQ\_MODE

When normal acquisition mode is used, the measure_complete_callback function is called only after the Touch Library completes processing of the signal values obtained. The references, sensor states and rotor/slider position values are updated in this mode.

11.3.12. Calibration Auto tune Setting (tag\_auto\_tune\_type\_t)

Touch library PTC prescaler clock and series resistor auto tuning setting

Data Fields

• AUTO_TUNE_NONE Auto tuning mode disabled. This mode uses the user defined PTC prescaler and series resistor values.
• AUTO_TUNE_PRSC Auto tune PTC prescaler for best noise performance. This mode uses the user defined series resistor value.
• AUTO_TUNE_RSEL Auto tune series resistor for least power consumption. This mode uses the user defined PTC prescaler value.

11.3.13. PTC Acquisition Frequency Mode Setting (tag\_freq\_mode\_sel\_t)

The frequency mode setting option enables the PTC acquisition to be configured for the following modes.

• Frequency hopping and spread spectrum disabled.
  • Frequency hopping enabled with median filter.
• Frequency spread spectrum enabled without median filter.
• Frequency spread spectrum enabled with median filter.

Range: FREQ_MODE_NONE (no frequency hopping & spread spectrum) to FREQ_MODE_SPREAD_MEDIAN (spread spectrum with median filter)

Data Fields

• FREQ_MODE_NONE 0u
• FREQ MODE HOP 1u
• FREQ_MODE_SPREAD 2u
• FREQ_MODE_SPREAD_MEDIAN 3u

11.3.14. PTC Clock Pre-scaler Setting (tag\_prsc\_div\_sel\_t)

Refer touch_configure_ptc_clock() API in touch.c

Example:

If generic clock input to PTC = 4 MHz,

• PRSC_DIV_SEL 1 sets PTC Clock to 4 MHz.
• PRSC_DIV_SEL 2 sets PTC Clock to 2 MHz.
• PRSC_DIV_SEL_4 sets PTC Clock to 1 MHz.
• PRSC_DIV_SEL_8 sets PTC Clock to 500 kHz.

Data Fields

• PRSC_DIV_SEL_1
PRSC_DIV_SEL_2
PRSC_DIV_SEL_4
PRSC_DIV_SEL_8

11.3.15. PTC Series Resistor Setting (tag\_rsel\_val\_t)

For mutual capacitance mode, this series resistor is switched internally on the Y-pin. For self-capacitance mode, the series resistor is switched internally on the sensor pin.

Example:

• RSEL_VAL_0 sets internal series resistor to 0 Ohms.
• RSEL VAL 20 sets internal series resistor to 20 Kohms.
• RSEL_VAL_50 sets internal series resistor to 50 Kohms.
• RSEL_VAL_100 sets internal series resistor to 100 Kohms.

Data Fields

RSEL_VAL_0
RSEL_VAL_20
RSEL_VAL_50
RSEL_VAL_100

11.3.16. PTC Acquisition Frequency Delay Setting (tag\_rsel\_val\_t)

The PTC acquisition frequency is dependent on the generic clock input to PTC and PTC clock prescaler setting. This delay setting inserts n PTC clock cycles between consecutive measurements on a given sensor, thereby changing the PTC acquisition frequency. FREQ_HOP_SEL_1 setting inserts 0 PTC clock cycle between consecutive measurements. FREQ_HOP_SEL_16 setting inserts 15 PTC clock cycles. Hence, higher delay setting will increase the total time required for capacitance measurement on a given sensor as compared to a lower delay setting.

A desired setting avoids noise in the same frequency as the acquisition frequency.

Data Fields

- FREQ_HOP_SEL_1
- FREQ_HOP_SEL_2
- FREQ_HOP_SEL_3
- FREQ_HOP_SEL_4
- FREQ_HOP_SEL_5
- FREQ_HOP_SEL_6
- FREQ_HOP_SEL_7
- FREQ_HOP_SEL_8
- FREQ_HOP_SEL_9
- FREQ_HOP_SEL_10
- FREQ_HOP_SEL_11
- FREQ_HOP_SEL_12
- FREQ_HOP_SEL_13
- FREQ_HOP_SEL_14
- FREQ_HOP_SEL_15
- FREQ_HOP_SEL_16 

11.3.17. AKS Group (tag\_aks\_group\_t)

It provides information about the sensors that belong to specific AKS group. NO_AKS_GROUP indicates that the sensor does not belong to any AKS group and cannot be suppressed. AKS_GROUP_x indicates that the sensor belongs to the AKS group x.

Data Fields

- NO_AKS_GROUP
- AKS_GROUP_1
- AKS_GROUP_2
- AKS_GROUP_3
- AKS_GROUP_4
- AKS_GROUP_5
- AKS_GROUP_6
- AKS_GROUP_7
- MAX_AKS_GROUP Max value of enum type for testing. 

11.3.18. Sensor Hysteresis Setting (tag\_hysteresis\_t)

A sensor detection hysteresis value. This is expressed as a percentage of the sensor detection threshold. HYST_x = hysteresis value is x% of detection threshold value (rounded down).

Note: A minimum value of 2 is used.

Example: If detection threshold = 20,

- HYST_50 = 10 (50% of 20)
- HYST_25 = 5 (25% of 20)
- HYST_12_5 = 2 (12.5% of 20)
- HYST_6_25 = 2 (6.25% of 20 = 1, but value is hard limited to 2) 

Data Fields

HYST_50 

HYST_25
HYST 12 5
HYST_6_25
- MAX_HYST Max value of enum type for testing.

11.3.19. Sensor Recalibration Threshold (tag\_recal\_threshold\_t)

This is expressed as a percentage of the sensor detection threshold. RECAL_x = recalibration threshold is x% of detection threshold value (rounded down).

Note: A minimum value of 4 is used.

Example: If detection threshold = 40,

• RECAL_100 = 40 (100% of 40)
• RECAL_50 = 20 (50% of 40)
  • RECAL 25 = 10 (25% of 40)
• RECAL 12 5 = 5 (12.5% of 40)
• RECAL_6_25 = 4 (6.25% of 40 = 2, but value is hard limited to 4)

Data Fields

• RECAL_100
  RECAL_50
• RECAL_25
• RECAL 12 5
  RECAL_6_25
• MAX_RECAL Max value of enum type for testing.

11.3.20. Rotor Slider Resolution (tag\_resolution\_t)

For rotors and sliders, the resolution of the reported angle or position.

- RES_x_BIT = rotor/slider reports x-bit values.

Example: If slider resolution is RES_7_BIT, then reported positions are in the range 0..127.

Data Fields

• RES_1_BIT
RES 2 BIT
RES 3 BIT
RES_4_BIT
RES_5_BIT
RES 6 BIT
RES 7 BIT
RES_8_BIT
- MAX_RES Max value of enum type for testing.

11.3.21. PTC Sensor Noise Lockout setting (nm\_sensor\_lockout\_t)

The sensor lockout setting option allows the system to be configured in the following modes.

• SINGLE_SENSOR_LOCKOUT Single sensor can be locked out.
  GLOBAL SENSOR LOCKOUT All the sensors are locked out for touch detection.
• NO_LOCK_OUT All the sensors are available for touch detection.

Range: SINGLE_SENSOR_LOCKOUT to NO_LOCK_OUT.

Data Fields

• SINGLE_SENSOR_LOCKOUT 0u
• GLOBAL_SENSOR_LOCKOUT 1u
- NO_LOCK_OUT 2u

11.3.22. 11\_3\_21\_PTC\_GPIO\_STATE(ptc\_gpio\_state\_t)

Detailed Description

PTC lines state in unmeasured condition can be set using this enum

• PULLHIGH WHEN NOT MEASURED Indicates that default state of PTC lines are at vcc.
GND WHEN NOT MEASURED Indicates that default state PTC lines are grounded.

Range: PULLHIGH_WHEN_NOT_MEASURED=0 and GND_WHEN_NOT_MEASURED.

Data Fields

• PULLHIGH_WHEN_NOT_MEASURED
GND_WHEN_NOT_MEASURED

11.3.23. Moisture Group Setting (moisture\_grp\_t)

Detailed Description

Sensor can be configured in the moisture group using this type.

• MOIS_DISABLED Indicates that the sensor does not belong to any moisture group.
• MOIS_GROUP_X Indicates that the sensor belongs to the moisture group x.

Range: MOIS_DISABLED = 0 to MOIS_GROUP_7.

Data Fields

• MOIS_DISABLED=0
  • MOIS_GROUP_0
  MOIS_GROUP_1
  MOIS_GROUP_2
  MOIS_GROUP_3
  MOIS_GROUP_4
  MOIS_GROUP_5
  MOIS_GROUP_6
  MOIS_GROUP_7
  MOIS_GROUPN

11.3.24. Multi-touch Group Setting (mltch\_grp\_t)

Detailed Description

Sensor can be configured in the multi-touch group using this type

• MLTCH_NONE Indicates that the sensor does not belong to any multi-touch group.
• MLTCH_GROUP_X Indicates that the sensor belongs to the multi-touch group x.

Range: MLTCH_NONE=0 to MOIS_GROUP_7.

Data Fields

MLTCH NONE=0
MLTCH GROUP 0
MLTCH_GROUP_1
MLTCH_GROUP_2
MLTCH_GROUP_3
MLTCH_GROUP_4
MLTCH_GROUP_5
MLTCH_GROUP_6
MLTCH_GROUP_7
MLTCH_GROUPN

11.3.25. Touch Mode Configuration (tag\_tch\_mode)

Touch mode can be configured.

Note: This is applicable only for ATmega devices.

Data Fields

• TCH_MODE_POLLED Polled mode
- TCH_MODE_ISR Interrupt mode
- TCH_MODE_NONE Touch mode is null.

11.3.26. Trigger Mode (tag\_trigger\_mode)

Trigger source for continuous hardware PTC acquisition. It is n clock cycles of internal 128Khz clock.

Note: This is applicable only for ATmega devices.

Data Fields

TCH_TRIGGER_128KHZ_4MS
TCH TRIGGER 128KHZ 8MS
TCH TRIGGER 128KHZ 16MS
TCH_TRIGGER_128KHZ_32MS
TCH TRIGGER 128KHZ 64MS
TCH TRIGGER 128KHZ 128MS
TCH_TRIGGER_128KHZ_256MS

11.4. Datastructures

11.4.1. Touch Library Timing Info (tag\_touch\_time\_t)

Touch library time parameter.

Data Fields

Field Unit Description
measurement_period_ms	uint16_t	Touch measurement period in milliseconds. This variable determines how often a new touch measurement must be done.
current_time_ms volatile	uint16_t	Current time set by timer ISR.
time_to_measure_touch	volatile uint8_t	Flag set by timer ISR when it is time to measure touch.

11.4.2. Sensor Info (tag\_sensor\_t)

Sensor structure for storing sensor related information.

Data Fields

Keyword Type Description
state uint8_t		Sensor state (calibrate, on, off, filter-in, filter-out, disable, pos-recal)
general_counter uint8_t		General purpose counter used for calibrating, drifting, etc
ndil_counter uint8_t		Counter used for detect integration
type_aks_pos_hyst	uint8_t	bits 7..6: sensor type: {00: key,01: rotor,10: slider,11: reserved} bits 5..3: AKS group (0..7): 0 = no AKS group bit 2 : positive recal flag bits 1..0: hysteresis
threshold uint8_t		Sensor detection threshold
from_channel uint8_t		Sensor from channel for keys: from channel = to channel. Rotors: Top channel. Sliders : Left most channelNote: We need to_channel for rotors/sliders only
to_channel uint8_t		For keys, this is unused. For rotors: Bottom left channel. For sliders: Middle channel
index uint8_t		Index into array of rotor/slider values

11.4.3. Global Sensor Configuration Info (tag\_touch\_global\_param\_t)

Touch library global parameter.

Data Fields

Field Unit Description
di	uint8_t	Detect Integration (DI) limit.
atch_drift_rate	uint8_t	Sensor away from touch drift rate.
tch_drift_rate	uint8_t	Sensor towards touch drift rate.
max_on_duration	uint8_t	MaximumON time duration.
drift_hold_time	uint8_t	Sensor drift hold time.
atch_recal_delay	uint8_t	Sensor away from touch recalibration delay.
cal_seq_1_count uint8_t		Sensor calibration dummy burst count.
cal_seq_2_count uint8_t		Sensor calibration settling burst count.
recal_threshold recal_threshold_d_t		Sensor away from touch recalibration threshold.
touch_postprocess_mode Uint16_t		Sensor post-processing mode.
auto_os_sig_stability_limit uint8_t		Stability limit for Auto Oversample feature.
auto_tune_sig_stability_limit uint16_t		Stability limit for frequency auto tune feature.
auto_freq_tune_in_cnt uint8_t		Frequency auto tune In counter.
nm_sig_stability_limit uint16_t		Stability limit for noise measurement.
nm_noise_limit uint8_t		Noise limit.
nm_enable_sensor_lock_out nm_sensor_lockout_t		Sensor lockout feature variable.
nm_lockout_countdown uint8_t		Lockout countdown for noise measurement.
Charge_share_delay uint8_t		Charge share delay value; applicable only for SAM C20, SAM C21, SAM L22 and ATmega devices.

11.4.4. Filter Callback Data Type (tag\_touch\_filter\_data\_t)

Touch library filter callback data type.

Data Fields

Field Unit Description
num_channel_signals	uint16_t	Length of the measured signal values list.
p_channel_signals	uint16_t	Pointer to measured signal values for each channel.

11.4.5. Measure Data Type (tag\_touch\_measure\_data\_t)

Touch library measure data type.

Data Fields

Field Unit Description
measurement_done_t ouch	volatile uint8_t	Flag set by touch_xxxxcap_measure_complete_callback() function when a latest Touch status is available.
acq_status touch_acq_status_t		Status of touch measurement.
num_channel_signals	uint16_t	Length of the measured signal values list.
*p_channel_signals	uint16_t	Pointer to measured signal values for each channel.
num_channel_refere nces	uint16_t	Length of the measured reference values list.
*p_channel_refere nces	uint16_t	Pointer to measured reference values for each channel.
num_sensor_states	uint8_t	Number of sensor state bytes.
*p_sensor_states	uint8_t	Pointer to touch status of each sensor.
num_rotor_slider_values	uint8_t	Length of the rotor and slider position values list.
*p_rotor_slider_values	uint8_t	Pointer to rotor and slider position values.
num_sensors	uint16_t	Length of the sensors data list.
*p_cc_calibration_vals	uint16_t	Pointer to calibrated compensation values for a given sensor channel.
*p_sensors	sensor_t	Pointer to sensor data.
*p_sensor_noise_status	uint8_t	Pointer to noise status of the sensors.
*p_nm_ch_noise_val	uint16_t	Pointer to noise level value of each channel.
*p_sensor_mois_status	uint8_t	Pointer to moisture status
*p_auto_os_status	uint8_t	Pointer to auto-oversamples status
cc_calib_status_flag	uint8_t	Flag is set when CC-calibration is ongoing.

11.4.6. Sensor Configuration Parameter

(tag_touch_selfcap_param_t, tag_touch_mutlcap_param_t)

Touch library self-capacitance and mutual capacitance sensor parameter.

Data Fields

Field Unit Description
aks_group aks_group_t		Which AKS group, the sensor belongs to.
detect_threshold threshold_t		An unsigned 8-bit number setting a sensor detection threshold.
detect_hysteresis hysteresis_t		A sensor detection hysteresis value. This is expressed as a percentage of the sensor detection threshold. HYST_x = hysteresis value is x% of detection threshold value (rounded down). A minimum value of 2 is used. Example: If detection threshold = 20, HYST_50= 10 (50% of 20)HYST_25= 5 (25% of 20)HYST_12_5 = 2 (12.5% of 20)HYST_6_25 = 2 (6.25% of 20 = 1, but value is hard limited to 2)
position_resolution	resolution_t	For rotors and sliders, the resolution of the reported angle or position. RES_x_BIT = rotor/slider reports x-bit values. Example: If slider resolution is RES_7_BIT, then reported positions are in the range 0..127
position_hysteresis	uint8_t	Sensor position hysteresis. This is valid only for a rotor or slider. bits 1..0: hysteresis.Note: This parameter is valid only for mutual capacitance method.

11.4.7. Sensor Acquisition Parameter

(tag_touch_selfcap_acq_param_t,_tag_touch_mutlcap_acq_param_t)

Sensor acquisition parameter.

Data Fields

Field Unit Description
*p_xxxxcap_gain_per_node gain_t		Pointer to gain per node.
touch_xxxxcap_freq_mode Freq_mode_sel_t		Set-up acquisition frequency mode.
*xxxxcap_ptc_prsc prsc_div_sel_t		Pointer to PTC clock pre-scaler value.
*xxxxcap_resistor_value rsel_val_t		Pointer to PTC series resistor value.
p_xxxxcap_hop_freqs *freq_hop_sel_t		Pointer to acquisition frequency settings.
*p_xxxxcap_filter_level filter_level_t		Pointer to filter level.
*p_xxxxcap_auto_os auto_os_t		Pointer to auto oversampling.
*xxxxcap_ptc_prsc_cc_cal prsc_div_sel_t		Pointer to PTC clock prescale value during CC calibration.
*xxxxcap_resistor_value_cc_cal	rsel_val_t	Pointer to PTC sense resistor value during CC calibration.

11.4.8. Self-capacitance Sensor Configuration (touch\_selfcap\_config\_t)

Touch Library self-capacitance configuration input type.

Data Fields

Field Unit Description
num_channels uint16_t		Number of channels.
num_sensors uint16_t		Number of sensors.
num_rotors_and_sliders uint8_t		Number of rotors/sliders.
global_param touch_global_param_t		Global sensor configuration information.
touch_selfcap_acq_param touch_selfcap_acq_param_t		Sensor acquisition parameter information.
*p_data_blk uint8_t		Pointer to data block buffer.
buffer_size uint16_t		Size of data block buffer.
*p_selfcap_y_nodes uint16_t		Pointer to self-capacitance nodes.
self_quick_reburst_enable uint8_t		Quick re-burst enable.
(touch_filter_data_t*p_filter_data)	void(*filter_callback)	Self-capacitance filter callback.
enable_freq_auto_tune uint8_t		Frequency auto tune enable.
enable_noise_measurement	uint8_t	Noise measurement enable.
nm_buffer_cnt	uint8_t	Memory allocation buffer.
self_mois_tlrnce_enable uint8_t		Self-capacitance moisture tolerance enable flag.
self_mois_groups	uint8_t	Number of self-capacitance moisture groups.
self_mois_quick_reburst_enable uint8_t	Moisture Quick re-burst enable.
self_ptc_gpio_state ptc_gpio_state_t	GPIO state for Self-capacitance PTC pins
tlib_feature_list tlib_init_fn_ptr	Library feature list.

11.4.9. Mutual Capacitance Sensor Configuration (touch\_mutlcap\_config\_t)

Touch Library mutual capacitance configuration input type.

Data Fields

Field Unit Description
num_channels uint16_t		Number of channels.
num_sensors uint16_t		Number of sensors.
num_rotors_and_sliders uint8_t		Number of rotors/sliders.
global_param touch_global_param_t		Noise measurement enable/disable.
touch_xxxxcap_acq_param touch_xxxxcap_acq_param_t		Sensor acquisition parameter info.
*p_data_blk uint8_t		Pointer to data block buffer.
*buffer_size uint16_t		Size of data block buffer.
*p_mut1cap_xy_nodes uint16_t		Pointer to xy-nodes.
mutl_quick_reburst_enable uint8_t		Quick re-burst enable.
(touch_filter_data_t*p_filter_data)	void(*filter_callback)	Mutual capacitance filter callback.
enable_freq_auto_tune uint8_t		Frequency auto tune enable.
enable_noise_measurement uint8_t		Noise measurement enable.
nm_buffer_cnt uint8_t		Memory allocation buffer.
mutl_mois_tlrnce_enable uint8_t		Mutual capacitance moisture tolerance enable flag.
mutl_mois_groups	uint8_t	Number of mutual capacitance moisture groups.
mutl_mois_quick_reburst_enable uint8_t	Moisture Quick re-burst enable.
mutl_ptc_gpio_state ptc_gpio_state_t	GPIO state for mutual capacitance PTC pins
tlib_feature_list tlib_init_fn_ptr	Library feature list.

11.4.10. Moisture Structure (tag\_snsr\_mois\_t)

Structure for storing moisture and multi-touch group information.

Data Fields

Field Unit Description
mois_grp uint8_t		Moisture group member
multch_grp uint8_t		Multi-touch group member

11.4.11. Touch Library Input Configuration (touch\_config\_t)

Touch Library Input Configuration Structure.

Data Fields

Field Unit Description
p_mutlcap_config	touch_mutlcap_config_t	Pointer to mutual capacitance configuration structure.
p_selfcap_config	touch_selfcap_config_t	Pointer to self-capacitance configuration structure.
ptc_isr_lvl	uint8_t	PTC ISR priority level.Note: This is applicable only for SAM devices.
tch_mode	tch_mode_t	Touch mode configuration.Note: This is applicable only for ATmega devices.

11.4.12. Library Function List (tag\_tlib\_init\_fn\_ptr\_t)

Touch Library support functions initializer.

Data Fields

Field	Unit	Description
auto_tune_init	void(*auto_tune_init)	Auto-tune function initializer
auto_os_init	uint32_t (*auto_os_init)	Auto-OS function initializer
lk_chk	void(*lk_chk)	Sensor lock-out function initializer
enable_aks	void enable_aks(void)	AKS function initializer

11.4.13. Touch Library Information (tag\_touch\_info\_t)

Touch Library information structure.

Data Fields

Field Unit Description
tlib_state touch_tlib_state_t		Touch library state is specified
num_channels_in_use unit16_t		Number of channels in use;irrespective of the corresponding sensor being disabled or enabled
num_sensors_in_use uint16_t		Number of sensors in use;irrespective of the sensor being disabled or enabled
num_rotors_sliders_in_use uint8_t		Number of rotor sliders in use;irrespective of the Rotor/Slider being disabled or enabled
max_channels_per_rotor_slider	uint8_t	Max possible number of channels per rotor or slider

11.4.14. Touch Library Version Information (touch\_libver\_info\_t)

Touch Library version information structure.

Data Fields

Field Unit Description
chip_id unit32_t		Chip ID
product_id uint16_t		Product ID
fw_version uint16_t		Touch Library VersionBits[12:15] ReservedBits[8:11]TLIB_MAJOR_VERSIONBits[4:7]TLIB_MINOR_VERSIONBits[0:3]TLIB_PATCH_VERSION

11.5. Global Variables

Field Unit	Description
touch_time	touch_time_t	This holds the library timing info
touch_acq_status	touch_acq_status_t	This holds the Touch Library acquisition status
cc_cal_max_signal_limit	uint16_t	CC calibration maximum signal limit variable
cc_cal_min_signal_limit	uint16_t	CC calibration minimum signal limit variable
Field Unit Description
*p_selfcap_measure_data	touch_measure_data_t	This holds the self-capacitance method measure data pointer
*p_mut1cap_measure_data	touch_measure_data_t	This holds the mutual capacitance method measure data pointer
wake_up_touch uint8_t		Wake up touch status from Library to Application
low_power_mode uint8_t		Low power mode status from Library to Application
mois_lock_global_mut1 uint8_t		Moisture global lock variable for mutual capacitance method
mois_lock_global_self uint8_t		Moisture global lock variable for self-capacitance method

11.6. API

11.6.1. Sensor Init and De-init

touch_ret_t touch_mutlcap_sensors_init (touch_config_t * p_touch_config)
touch_ret_t touch_selfcap_sensors_init (touch_config_t * p_touch_config) 

This API is used to initialize the Touch Library with Mutual cap or Self cap method pin, register and sensor configuration provided by the user.

Parameters: p_touch_config Pointer to Touch configuration structure.

Returns:touch_ret_t: Touch Library Error status.

touch_ret_t touch_mutlcap_sensors_deinit(void)
touch_ret_t touch_selfcap_sensors_deinit(void); 

This API can be used to de-initialize the sensor for specific sensing group.

Parameters:

void.

Returns:

touch_ret_t: Touch Library Error status.

11.6.2. Sensor Setup and Configuration

touch_ret_t touch_mutIcap_sensor_config (sensor_type_t sensor_type, channel_t from_channel, channel_t to_channel, aks_group_t aks_group, threshold_t detect_threshold, hysteresis_t detect_hysteresis, resolution_tposition_resolution, uint8_t position_hysteresis, sensor_id_t *p_sensor_id) 

touch_ret_t touch_selfcap_sensor_config (sensor_type_t sensor_type, channel_t from_channel, channel_t to_channel, aks_group_t aks_group, threshold_t detect_threshold, hysteresis_t detect_hysteresis, resolution_t position_resolution, sensor_id_t * p_sensor_id) 

This API can be used to configure a sensor of type key, rotor or slider.

Data Fields:

Field Description
sensor_type	can be of type key, lump, rotor, or slider.
from_channel	the first channel in the slider sensor.
to_channel	the last channel in the slider sensor.
aks_group	which AKS group (if any) the sensor is in.
detect_threshold	the sensor detection threshold.
detect_hysteresis	the sensor detection hysteresis value.
position_resolution	the resolution of the reported position value.
position_hysteresis	the hysteresis for position value (available only for mutual capacitance mode).
p_sensor_id	the sensor id value of the configured sensor is updated by the Touch Library.

Returns: touch_ret_t: Touch Library Error status.

11.6.3. Sensor Calibration

touch_ret_t touch_mutlcap_sensors_calibrate (auto_tune_type_t)
touch_ret_t touch_selfcap_sensors_calibrate (auto_tune_type_t) 

This API is used to calibrate the sensors for the first time before starting a Touch measurement. This API can also be used to force calibration of sensors when any of the Touch sensor parameters are changed during runtime.

Returns:touch_ret_t: Touch Library Error status.

11.6.4. Sensor Measure

touch_ret_t touch_mutlcap_sensors_measure (touch_current_time_t current_time_ms, touch_acq_mode_tmutlcap_acq_mode, void(*) (void) measure_complete_callback) 

touch_ret_t touch selfcap sensors measure (touch current time t current time ms, touch acq mode tselfcap acq mode, void(*) (void) measure complete callback) 

This API can be used to start a Touch measurement.

Parameters:

current_time_ms Current time in millisecond.

measure_complete_callback Interrupt callback to indicate measurement completion.

Returns:

touch_ret_t: Touch Library Error status.

11.6.5. Sensor Suspend and Resume

touch_ret_t touch_suspend_ptc(void) 

touch_ret_t touch_resume_ptc(void) 

The touch_suspend_ptc function suspends the PTC library's current measurement cycle. The completion of the operation is indicated through callback pointer that must be initialized by the application. Refer Sensor Global Parameters.

The touch_resume_ptc function resumes the PTC library's current measurement which was suspended using touch_suspend_ptc. After the touch_resume_ptc function is called by the application, the touch_xxxxcap_sensors_measure API should be called only after the measurement complete callback function is received.

Parameters:

void.

Returns:

touch_ret_t: Touch Library Error status.

11.6.6. Sensor Disable and Re-enable

touch_ret_t touch_mutlcap_sensor_disable (sensor_id_t sensor_id)
touch_ret_t touch_selfcap_sensor_disable (sensor_id_t sensor_id) 

This API can be used to disable any sensor.

Parameters:

sensor_id Sensor number which needs to be disabled

Returns:

touch_ret_t: Touch Library Error status.

touch_ret_t touch_muticap_sensor_reenable (sensor_id_t sensor_id, uint8_t no_calib) 

touch_ret_t touch_selfcap_sensor_reenable (sensor_id_t sensor_id, uint8_t no_calib) 

This API can be used to re-enable a disabled sensor.

Parameters:

sensor_id Sensor number which needs to be reenabled

no_calib When value is set to 1, force calibration is not applicable. When value is set to 0, force calibration is applied

Returns:

touch_ret_t: Touch Library Error status.

11.6.7. Read-back Sensor Configuration

touch_ret_t touch_mutlcap_sensor_get_acq_config (touch_mutlcap_acq_param_t *p_touch_mutlcap_acq_param) 

touch_ret_t touch_selfcap_sensor_get_acq_config (touch_selfcap_acq_param_t *p_touch_selfcap_acq_param) 

This API can be used to read back the sensor acquisition parameters.

Parameters:

p_touch_mutlcap_acq_param The acquisition parameters for the mutual capacitance.

p_touch_selfcap_acq_param The acquisition parameters for the self-capacitance.

Returns:

touch_ret_t: Touch Library Error status.

touch_ret_t touch_mutlcap_sensor_get_config (sensor_id_t sensor_id, touch_mutlcap_param_t *p_touch_sensor_param) 

touch_ret_t touch_selfcap_sensor_get_config (sensor_id_t sensor_id, touch_selfcap_param_t *p_touch_sensor_param) 

This API can be used to read back the sensor configuration parameters.

Parameters:

sensor_id The sensor id for which the parameters has to be read-back.

p_touch_sensor_param The sensor parameters for the mutual or self-capacitance.

Returns:

touch_ret_t: Touch Library Error status.

touch_ret_t touch_mutlcap_sensor_get_delta (sensor_id_t sensor_id, touch_delta_t * p_delta) 

touch_ret_t touch_selfcap_sensor_get_delta (sensor_id_t sensor_id, touch_delta_t * p_delta) 

This API can be used to retrieve the delta value corresponding to a given sensor.

Parameters:

sensor_id The sensor id for which delta value is being seeked.

p_delta Pointer to the delta variable to be updated by the Touch Library.

Returns:

touch_ret_t: Touch Library Error status.

touch_ret_t touch_mutlcap_get_global_param (touch_global_param_t * p_global_param) 

touch_ret_t touch_selfcap_get_global_param (touch_global_param_t * p_global_param) 

This API can be used to read back the global parameter.

Parameters:

p_global_param The pointer to global sensor configuration.

Returns:

touch_ret_t: Touch Library Error status.

11.6.8. Update Sensor Configuration

touch_ret_t touch_mutlcap_sensor_update_acq_config (touch_mutlcap_acq_param_t *p_touch_mutlcap_acq_param) 

touch_ret_t touch_selfcap_sensor_update_acq_config (touch_selfcap_acq_param_t *p_touch_selfcap_acq_param) 

This API can be used to update the sensor acquisition parameters.

Parameters:

p_touch_mutlcap_acq_param The acquisition parameters for the mutual capacitance.

p_touch_selfcap_acq_param The acquisition parameters for the self-capacitance.

Returns:

touch_ret_t: Touch Library Error status.

touch_ret_t touch_mutlcap_sensor_update_config (sensor_id_t sensor_id, touch_mutlcap_param_t *p_touch_sensor_param) 

touch_ret_t touch_selfcap_sensor_update_config (sensor_id_t sensor_id, touch_selfcap_param_t *p_touch_sensor_param 

This API can be used to update the sensor configuration parameters.

Parameters:

sensor_id The sensor id whose configuration parameters has to be changed.

p_touch_sensor_param The touch sensor parameter structure that will be used by the Touch Library to update.

Returns:

touch_ret_t: Touch Library Error status.

touch_ret_t touch_mutlcap_update_global_param (touch_global_param_t * p_global_param) 

touch ret t touch selfcap update global param (touch global param t * p global param) 

This API can be used to update the global parameter.

Parameters:

p_global_param The pointer to global sensor configuration.

Returns:

touch_ret_t: Touch Library Error status.

11.6.9. Get Library Information and Version

touch_ret_t touch_mutlcap_get_libinfo (touch_info_t * p_touch_info) 

touch_ret_t touch_selfcap_get_libinfo (touch_info_t * p_touch_info) 

This API can be used to get the Touch Library configuration.

Parameters:

p_touch_info Pointer to the Touch info data structure that will be updated by the Touch Library.

Returns:

touch_ret_t: Touch Library Error status.

touch_ret_t touch_library_get_version_info (touch_libver_info_t * p_touch_libver_info) 

This API can be used to get the Touch Library version information.

Parameters:

p_touch_libver_info Pointer to the Touch Library Version info data structure that will be updated by the Touch Library.

11.6.10. Moisture Tolerance API

touch_ret_t touch_mutlcap_cnfg_mois_mltchgrp(sensor_id_t snsr_id, moisture_grp_t mois_grpid, mltch_grp_t mltch_grpid) 

touch_ret_t touch_selfcap_cnfg_mois_mltchgrp(sensor_id_t ansr_id, moisture_grp_t mois_grpid, mltch_grp_t mltch_grpid) 

This API can be used to assign moisture group and multi touch group for a sensor.

Parameters:

snsr_id - sensor ID

mois_grpid - moisture group ID

mltch_grp_t - multi-touch group

Returns:

touch_ret_t: Touch Library Error status.

touch_ret_t touch_mutlap_cnfq_mois_threshold(moisture_grp_t mois_grpid, mois_snsr_threshold_t snsr_threshold, mois_system_threshold_t system_threshold) 

touch_ret_t touch_selfcap_cnfg_mois_threshold(moisture_grp_t mois_grpid, mois_snsr_threshold_t snsr_threshold, mois_system_threshold_t system_threshold) 

This API is used to assign moisture sensor threshold and moisture system threshold to a moisture group ID

Parameters:

mois_grpid - moisture group ID

snsr_threshold - moisture sensor threshold

system_threshold - moisture system threshold

Returns:

touch_ret_t: Touch Library Error status.

touch_ret_t touch_mutlcap_mois_tolrnce_enable(void)
touch_ret_t touch_selfcap_mois_tolrnce_enable(void) 

This API is used to enable moisture tolerance check during run time.

Returns:

touch_ret_t: Touch Library Error status.

touch_ret_t touch_mutlcap_mois_tolrnce_quick_reburst_enable(void)
touch_ret_t touch_selfcap_mois_tolrnce_quick_reburst_enable(void) 

This API is used to enable moisture tolerance quick re-burst feature during run time.

Returns:

touch_ret_t: Touch Library Error status.

touch_ret_t touch_mutlcap_mois_tolrnce_disable(void)
touch_ret_t touch_selfcap_mois_tolrnce_disable(void) 

This API is used to disable moisture tolerance check during run time.

Returns:

touch_ret_t: Touch Library Error status.

touch_ret_t touch_mutlcap_mois_tolrnce_quick_reburst_disable(void)
touch_ret_t touch_selfcap_mois_tolrnce_quick_reburst_disable(void) 

This API is used to disable moisture tolerance quick re- burst feature during run time.

Returns:

touch_ret_t: Touch Library Error status.

1. Revision History

Doc. Rev. Date	Comments
Rev.M 07/2016	1. Updated the latest software version numbers in Section 12. Added a new errata in Section 9
Rev.L 04/2016	Updated Sections 1, 5, and 8 with reference to the latest extension release
Rev.K 02/2016	Added ATmega324PB support.Updated Sections 1, 5 and 8 with reference to the latest extension release
Rev.J 01/2016	Included the following new sections:1. Compensation Circuit2. Using Atmel ICE for Qdebug Data Streaming3. Application flow for megaAVRUpdated Sections 5 and 8 with reference to the latest extension release
Rev.I 09/2015	Included Charge share delayUpdated Section 5 .2.8 and 5.2.10 - Library parameters for quick re-burst and moisture parameters addedUpdated Section 11.6.8 - Moisture API's AddedUpdated section 8 - Example projects updated
Rev.H 06/2015	Revised Section 2 - Device Variants Supported and included information on device multiplexing optionUpdated Section 7.2 - Code and data memory considerationsUpdated Section 5.2.1 - Pin, Channel, and Sensor Parameters
Rev.G 04/2015	Updated Section 2 - Device Variants Supported and included information on device multiplexing option
Rev.F 02/2015	Included relevant information regarding low-power and lumped mode support
Rev.E 11/2014	Included Section 5.2.6 and 5.2.7 regarding noise counter measures.Included Section 3 regarding overview of capacitive touch technology.
Rev.D 02/2014	Global updates across the document related to QTouch Library and QTouch Composer 5.3
Rev.C 10/2013	Included Section 3.3.4, Using QDebug Touch Data Debug CommunicationIncluded a note on interrupt handler for IAR example project in Section 3.3.3

Doc. Rev. Date Comments

Rev.B 10/2013 Updated errata in Section 4, Known Issues

Rev.A 09/2013 Initial document release

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