DSC2110 - Microcontroller Microchip - Free user manual and instructions

USER MANUAL DSC2110 Microchip

Programming User's Guide

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© 2018, Microchip Technology Incorporated, All Rights Reserved. ISBN: 978-1-5224-2887-9

Table of Contents

Preface ....5

Introduction 5

Document Layout 5

Conventions Used in this Guide 6

The Microchip Website 7

Customer Support 7

Document Revision History 7

Chapter 1. Product Overview ......9

Device Architecture 9

Default Conditions 9

Chapter 2. Programming Features ....11

Programming Clock Frequencies 11

Calculation of N,F & M for Single-Output Oscillator (DSC21X0 & DSC22X0) 11

Calculation of N,F & M for Single-Output Oscillator (DSC21X0 & DSC22X0) 13

Programming CMOS Output Drive Strength & Output Control Modes.... 15

Hibernate (Low Current) Mode.... 15

I^2C Bus Control Interface 15

SPI Bus Control Interface.... 17

Worldwide Sales and Service 29

NOTES:

Preface

NOTICE TO CUSTOMERS

All documentation becomes dated, and this manual is no exception. Microchip tools and documentation are constantly evolving to meet customer needs, so some actual dialogs and/or tool descriptions may differ from those in this document. Please refer to our web site (www.microchip.com) to obtain the latest documentation available.

Documents are identified with a "DS" number. This number is located on the bottom of each page, in front of the page number. The numbering convention for the DS number is "DSXXXXXXXXA", where "XXXXXXX" is the document number and "A" is the revision level of the document.

For the most up-to-date information on development tools, see the MPLAB ^® IDE online help. Select the Help menu, and then Topics to open a list of available online help files.

INTRODUCTION

This chapter contains general information that will be useful to know before using the DSC22XX/DSC21XX Programming Guide. Items discussed in this chapter include:

• Document Layout
  • Conventions Used in this Guide
  • The Microchip Website
• Customer Support
  • Document Revision History

DOCUMENT LAYOUT

This document describes how to use the DSC22XX/DSC21XX Programming Guide to program a MEMS oscillator device. The manual layout is as follows:

• Chapter 1. "Product Overview" – Provides important information about the DSC22XX/DSC21XX Programming Guide.
• Chapter 2. "Programming Features" – Provides information about using the DSC22XX/DSC21XX Programming Guide.

CONVENTIONS USED IN THIS GUIDE

This manual uses the following documentation conventions:

DOCUMENTATION CONVENTIONS

Description Represents Examples
Arial font:
Italic characters Referenced books	oks MPLAB	^ IDE User's Guide
	Emphasized text ...is the only compiler...
Initial caps A window the Output	window
	A dialog the Settings dialog
	A menu selection select Enable	Programmer
Quotes A field name in a window or dialog		"Save project before build"
Underlined, italic text with right angle bracket	A menu path File>Save	——
Bold characters A dialog button	Click OK
	A tab	Click the Power tab
N'Rnnnn	A number in verilog format, where N is the total number of digits, R is the radix and n is a digit.	4'b0010, 2'hF1
Text in angle brackets <>	A key on the keyboard	Press,,
Courier New font:
Plain Courier New	Sample source code	#define START
	Filenames	autoexec.bat
	File paths	c:\mccl8\h
	Keywords	_asm, _endasm, static
	Command-line options	-Opa+, -Opa-
	Bit values	0, 1
	Constants	0xFF, 'A'
Italic Courier New	A variable argument	file.o, where file can be any valid filename
Square brackets []	Optional arguments	mccl8 [options] file [options]
Curly brackets and pipe character: { | }	Choice of mutually exclusive arguments; an OR selection	errorlevel {0|1}
Ellipses...	Replaces repeated text	var_name [, var_name...]
	Represents code supplied by user	void main (void) { ... }

THE MICROCHIP WEBSITE

Microchip provides on-line support via our web site at www.microchip.com. This website is used as a means to make files and information easily available to customers. Accessible by using your favorite Internet browser, the website contains the following information:

• Product Support – Data sheets and errata, application notes and sample programs, design resources, user's guides and hardware support documents, latest software releases and archived software
• General Technical Support – Frequently Asked Questions (FAQs), technical support requests, on-line discussion groups, Microchip consultant program member listing
• Business of Microchip – Product selector and ordering guides, latest Microchip press releases, listing of seminars and events, listings of Microchip sales offices, distributors and factory representatives

CUSTOMER SUPPORT

Users of Microchip products can receive assistance through several channels:

• Distributor or Representative
- Local Sales Office
• Field Application Engineer (FAE)
- Technical Support

Customers should contact their distributor, representative or field application engineer (FAE) for support. Local sales offices are also available to help customers. A listing of sales offices and locations is included in the back of this document.

Technical support is available through the web site at: http://support.microchip.com.

DOCUMENT REVISION HISTORY

Revision A (April 2018)

- Converted Micrel version of the DSC22XX/DSC21XX Programming Guide to Microchip User Guide DS50002739A.

NOTES:

Chapter 1. Product Overview

1.1 DEVICE ARCHITECTURE

The DSC21XX & DSC22XX families of low jitter, configurable single and dual output oscillators consist of a MEMS resonator and a high performance PLL IC, programmable via I²C/SPI interface. This document will explain how to program the output frequencies as well as the CMOS outputs drive strength.

The basic block diagram of the dual and single output oscillators including the integrated PLL and clock distribution path are shown in Figure 1-1 and Figure 1-2. These oscillators are equipped with a high performance fractional-N PLL that locks an integrated high frequency VCO to the internal MEMS oscillator. The output of the VCO is then divided down through independent even integer dividers, with divide values ranging from 4 to 254, to generate the desired output clock frequencies. Each clock output is buffered by a low-noise output driver, available in CMOS, LVPECL, LVDS, and HCSL formats.

Block Diagrams of Single and Dual Output DSC20XX Oscillators

graph LR
    A["F_REF"] --> B["×"]
    B --> C["÷"]
    C --> D["×"]
    D --> E["F_VCO"]
    E --> F["÷M"]
    F --> G["÷2"]
    G --> H["OE"]
    H --> I["F_OUT"]
    J["÷N.F"] --> B
    K["M'"] --> F

FIGURE 1-1: Single Output Oscillator.

graph LR
    A["F_REF"] --> B["×"]
    B --> C["¬"]
    C --> D["¬"]
    D --> E["F_VCO"]
    E --> F["÷M1"]
    F --> G["÷2"]
    G --> H["O1E"]
    H --> I["F_OUT1"]
    D --> J["÷N.F"]
    J --> K["M2'"]
    K --> L["÷M2"]
    L --> M["÷2"]
    M --> N["O2E"]
    N --> O["F_OUT2"]

FIGURE 1-2: Dual Output Oscillator.

1.2 DEFAULT CONDITIONS

Upon power-up, the initial output frequency configuration is controlled by an internal preprogrammed memory (OTP). This memory stores all coefficients required by the PLL for two independent default frequencies for a single output oscillator, or two fre-

quency combinations for a dual output version. The control pin (FS) selects which default frequency is the initial setting. After power-up, a new output frequency configuration can be programmed using I ^2 C/SPI interface.

The CMOS output drive strength, which is programmable using 3 control bits, is set by default to maximum strength or the value of 111. After power-up, a new CMOS drive-strength setting can be programmed using I ^2 C/SPI interface.

Chapter 2. Programming Features

2.1 PROGRAMMING CLOCK FREQUENCIES

This section describes the PLL variables and registers used to configure the oscillator to produce the desired output frequencies.

As shown in Figure 1-1 and Figure 1-2, several parameters need to be programmed to determine the internal VCO and the output clock frequencies. The PLL consists of a feedback divider with a fractional value described as N.F, where N (7-bit value) and F (17-bit value) are the integer and fractional portions of the divider value, respectively. The PLL is then followed by M divider (8-bit value) integer divider and a final divide-by-2 stage to ensure 50% output clock duty cycle. The combination of these two dividers creates an even integer M' divider block with divider value range of 4 to 254. It must be noted that M must have a minimum value of 2. To summarize, the output frequency is specified by three programmable values, N, F & M.

2.1.1 Calculation of N,F & M for Single-Output Oscillator (DSC21X0 & DSC22X0)

To optimize performance of the PLL, it is desirable to program the internal PLL to the lowest possible valid VCO frequency that can generate the desired output clock frequency. The minimum valid VCO frequency for the device is 1135 MHz while the optimum VCO frequency range is from 1175 to 1700 MHz. Below is an example illustrating how to calculate the required N, F & M values.

Example:

Desired Clock Frequency: F_OUT = 25 MHz

Lowest Optimum VCO Frequency: F_VCO = F_OUT × M' = 25 × 48 = 1200 MHz

$$ M = M ^ {\prime} \div 2 = 2 4 $$

Once the VCO frequency is determined, the N.F value can be easily calculated by dividing the VCO frequency by the input reference frequency from the MEMS oscillator, which is calibrated in the fabrication process to 18 MHz.

$$ N. F = F _ {V C O} \div F _ {R E F} = 1 2 0 0 \mathrm{MHz} \div 1 8 \mathrm{MHz} = 6 6. 6 6 6 6 6 7 $$

$$ N = 6 6, F = 0. 6 6 6 6 6 7 $$

Since F is described using a 17-bit register, we need to calculate it as the numerator value that will create our desired fraction with (2^37 - 1) in the denominator. This number will then need to be rounded to the nearest integer value.

$$ F [ 1 6: 0 ] = 0. 6 6 6 6 6 7 \times (2 ^ {1 7} - 1) = 8 7 3 8 0. 7 1 \rightarrow F [ 1 6: 0 ] = 8 7 3 8 1 (\text { rounded }) $$

The final step before programming the values into the appropriate registers is to convert M, N, and F to the appropriate binary or hexadecimal values.

$$ M [ 7: 0 ] = 2 4 _ {\text { dec }} = 0 0 0 1 1 0 0 0 \text { bin } = 1 8 _ {\text { hex }} $$

$$ N [ 6: 0 ] = 6 6 _ {\text { dec }} = 1 0 0 0 0 1 0 1 \text { bin } = 8 5 _ {\text { hex }} $$

$$ F [ 1 6: 0 ] = 8 7 3 8 1 _ {\text { dec }} = 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 \text { bin } = 1 5 5 5 5 _ {\text { hex }} $$

We now load the resulting values into the appropriate registers to program the DSC21X0 or DSC22X0 to the desired output clock frequency. Table 2-1 describes the register map for the variables described above.

TABLE 2-1: REGISTER MAP FOR THE SINGLE-OUTPUT DSC2XXX OSCILLATOR

Register	7 6 5 4 3 2	1 0
0x13	F[7]	F[6]	F[5]	F[4]	F[3]	F[2]	F[1]	F[0]
0x14	F[15]	F[14]	F[13]	F[12]	F[11]	F[10]	F[9]	F[8]
0x15	N[6]	N[5]	N[4]	N[3]	N[2]	N[1]	N[0]	N[16]
0x16	M1[7]	M1[6]	M1[5]	M1[4]	M1[3]	M1[2]	M1[1]	M1[0]

Note: In reference to Register 0x13: Register 0x13 holds the least eight significant bits of the 17-bit F value. This register, though, is not accessible through the I²C and no writes should be made to it. While some frequency granularity is lost in programming only the upper 8 bits of F, frequency steps of about 13 ppm can be achieved, sufficiently fine for most applications.

Commonly used clock frequencies:

Table 2-2 provides a list of commonly used output clock frequencies, corresponding PLL variables, and register parameters that need to be programmed into the oscillator via I²C/SPI interface.
TABLE 2-2: COMMON CLOCK FREQUENCIES AND CORRESPONDING PARAMETERS

Freq (MHz)	M	N	F	FVCO (MHz)	Registers (address & value in HEX)
					0x13	0x14	0x15	0x16
19.2	31	66	0.133333	1190.4000	44	44	84	1F
24	25	66	0.666667	1200.0000	55	55	85	19
25	24	66	0.666667	1200.0000	55	55	85	18
33.3333	18	66	0.666666	1200.0000	55	55	85	12
40	15	66	0.666667	1200.0000	55	55	85	15
48	13	69	0.333333	1248.0000	AA	AA	8A	0D
50	12	66	0.666667	1200.0000	55	55	85	0C
54	11	66	0	1188.0000	00	00	84	0B
62.5	10	69	0.444444	1250.0000	8E	E3	8A	0A
66.6666	9	66	0.666666	1200.0000	55	55	85	09
74.25	8	66	0	1188.0000	00	00	84	08
75	8	66	0.666667	1200.0000	55	55	85	08
77.76	8	69	0.12	1244.1600	71	3D	8A	08
100	6	66	0.666667	1200.0000	55	55	85	06
106.25	6	70	0.833333	1275.0000	AA	AA	8D	06
125	5	69	0.444444	1250.0000	8E	E3	8A	05
133.333	5	74	0.074074	1333.3333	ED	25	94	05
148.5	4	66	0	1188.0000	00	00	84	04
150	4	66	0.666667	1200.0000	55	55	85	04
155.52	4	69	0.12	1244.1600	71	3D	8A	04
156.25	4	69	0.444444	1250.0000	8E	E3	8A	04
200	3	66	0.666667	1200.0000	55	55	85	03
212.5	3	70	0.833333	1275.0000	AA	AA	8D	03
400	2	88	0.888889	1600.0000	1C	C7	B1	02

2.1.2 Calculation of N,F & M for Dual-Output Oscillator (DSC21XX & DSC22XX)

Calculation of the PLL parameters (N, F & M) for the dual output oscillator devices is very similar to that described in the previous section. However, the oscillator will now need to simultaneously generate two output clock frequencies from a single VCO frequency. This constraint alters the computation of the common VCO frequency. We need a valid VCO frequency that when divided by two independent even integer values, each ranging from 4 to 254, will generate both desired output clock frequencies. This analysis is best performed with an iterative approach using a spreadsheet.

Example:

Desired Clock Frequency 1: F_OUT1 = 125 MHz

Desired Clock Frequency 2: F_OUT2 = 25 MHz

Lowest Common VCO Frequency (from spreadsheet): F_VCO = 1250 MHz

Once the VCO frequency is determined, all other parameters can be easily calculated as shown in previous section.

Example:

$$ \mathrm{M} 1 ^ {\prime} = \mathrm{F} _ {\mathrm{VCO}} \div \mathrm{F} _ {\mathrm{OUT} 1} = 1 2 5 0 \mathrm{MHz} \div 1 2 5 \mathrm{MHz} = 1 0 $$

$$ M 1 = M 1 ^ {\prime} \div 2 = 5 $$

And

$$ \mathrm{M} 2 ^ {\prime} = \mathrm{F} _ {\mathrm{VCO}} \div \mathrm{F} _ {\mathrm{OUT2}} = 1 2 5 0 \mathrm{MHz} \div 2 5 \mathrm{MHz} = 5 0 $$

$$ \mathrm{M} 2 = \mathrm{M} 2 ^ {\prime} \div 2 = 2 5 $$

$$ N. F = F _ {V C O} \div F R E F = 1 2 5 0 \mathrm{MHz} \div 1 8 \mathrm{MHz} = 6 9. 4 4 4 4 4 4 $$

$$ N = 6 9, F = 0. 4 4 4 4 4 4 $$

Since F is described using a 17-bit register, we need to calculate it as the numerator value that will create our desired fraction with (2^17 - 1) as the denominator. This number will then need to be rounded to the nearest integer value.

$$ F [ 1 6: 0 ] = 0. 4 4 4 4 4 4 \times (2 1 7 - 1) = 5 8 2 5 3. 7 1 \rightarrow F [ 1 6: 0 ] = 5 8 2 5 4 (\text { rounded }) $$

The final step before programming the values into the appropriate registers is to convert the M, N, and F to the appropriate binary or hexadecimal values.

$$ \mathrm{M} 1 [ 7: 0 ] = 5 _ {\text { dec }} = 0 0 0 0 0 1 0 1 _ {\text { bin }} = 0 5 _ {\text { hex }} $$

$$ \mathrm{M} 2 [ 7: 0 ] = 2 5 _ {\text {dec}} = 0 0 0 1 1 0 0 1 _ {\text {bin}} = 1 9 _ {\text {hex}} $$

$$ N [ 6: 0 ] = 6 9 _ {\text { dec }} = 1 0 0 0 1 0 1 0 _ {\text { bin }} = 8 A _ {\text { hex }} $$

$$ F [ 1 6: 0 ] = 5 8 2 5 4 _ {\text { dec }} = 0 1 1 1 0 0 0 1 1 1 0 0 0 1 1 1 0 _ {\text { bin }} = 0 E 3 8 E _ {\text { hex }} $$

We now load the resulting values into the appropriate registers to program the DSC21XX or DSC22XX to our desired output clock frequencies. Table 2-3 describes the register map for the variable described above.

TABLE 2-3: REGISTER MAP FOR THE DUAL-OUTPUT DSC21XX & DSC22XX OSCILLATORS

R	e	g	i	s	t	e	r	7	6
0x13	F[7]	F[6]	F[5]	F[4]	F[3]	F[2]	F[1]	F[0]
0x14	F[15]	F[14]	F[13]	F[12]	F[11]	F[10]	F[9]	F[8]
0x15	N[6]	N[5]	N[4]	N[3]	N[2]	N[1]	N[0]	N[16]
0x16	M1[7]	M1[6]	M1[5]	M1[4]	M1[3]	M1[2]	M1[1]	M1[0]
0x17	M2[7]	M2[6]	M2[5]	M2[4]	M2[3]	M2[2]	M2[1]	M2[0]

Note: In reference to Register 0x13: Register 0x13 holds the least eight significant bits of the 17-bit F value. This register, though, is not accessible through the I²C and no writes should be made to it. While some frequency granularity is lost in programming only the upper 8 bits of F, frequency steps of about 13 ppm can be achieved, sufficiently fine for most applications.

Commonly used clock frequencies:

Table 4 provides a list of commonly used output clock frequency combinations, corresponding PLL variables, and register values that need to be programmed into the oscillator via I ^2 C/SPI interface.

Contact factory for frequency pairs not included in the table below.

TABLE 2-4: COMMON CLOCK FREQUENCY PAIRS AND CORRESPONDING PARAMETERS

Freq1 (MHz)	Freq2 (MHz)	M1	M2 N	F		FVCO (MHz)	Registers (address & value in HEX)
							0x13	0x14 0x1	5 0x16	0x17
27	24	24	27	72	0	1296.0000	00	00	90	18	1B
27	25	25	27	75	0	1350.0000	00	00	96	19	1B
33.3333	25	18	24	66	0.66666	1199.0000	54	55	85	12	18
40	25	15	24	66	0.66667	1200.0000	55	55	85	0F	18
50	25	12	24	66	0.66667	1200.0000	55	55	85	0C	18
75	25	8	24	66	0.66667	1200.0000	55	55	85	08	18
100	25	6	24	66	0.66667	1200.0000	55	55	85	06	18
106.25	25	8	34	94	0.44444	1700.0000	8E	E3	BC	08	22
125	25	5	25	69	0.44444	1250.0000	8E	E3	8A	05	19
150	25	4	24	66	0.66667	1200.0000	55	55	85	04	18
156.25	25	4	25	69	0.44444	1250.0000	8E	E3	8A	04	19
212.5	25	4	34	94	0.44444	1700.0000	8E	E3	BC	04	22
40	33.3333	20	24	88	0.88889	1600.0000	1C	C7	B1	14	18
48	40	15	18	80	0	1440.0000	00	00	A0	0F	12
100	75	6	8	66	0.66667	1200.0000	55	55	85	06	08
50	106.25	17	8	94	0.44444	1700.0000	8E	E3	BC	11	08
50	125	15	6	83	0.33333	1500.0000	AA	AA	A6	0F	06
148.5	74.25	5	10	82	0.5	1485.0000	00	00	A5	05	0A
156.25	125	4	5	69	0.44444	1250.0000	8E	E3	8A	04	05

2.1.3 Executing a Frequency WRITE for (DSC21XX & DSC22XX)

When executing a frequency WRITE to the DSC21XX & DSC22XX devices it is required to place the device in Hibernate by setting (0x10h<5>), execute the frequency WRITE to addresses x13-x17h, then bring the device out of Hibernate by clearing (0x10h<5>). Refer to section 5 for details of entering/exiting Hibernate mode. Allow a 100 μs delay after applying the Hibernate signal before taking the subsequent Read / Write activity with the device.

The DSC21xx/22xx devices come with pre-stored frequencies selectable by the FSEL pin (pin 14). Frequency-bank 0 registers, selected when FSEL = 0, can be overwritten via I²C/SPI (addresses 0x13 - 0x17). Frequency-bank 1, selected when FSEL = 1, contains fixed frequency information and cannot be modified via I²C/SPI.

FSEL pin (pin 14) can be overwritten by resetting all the eight bits of register 0x12. Resetting register 0x12 makes the device select frequency-bank 0 and therefore allows the I²C/SPI interface to change the output frequency.

2.2 PROGRAMMING CMOS OUTPUT DRIVE STRENGTH & OUTPUT CONTROL MODES

As described earlier, drive strength for CMOS output drivers can be optimized via I^2C/SPI interface to help reduce EMI and improve performance. Each CMOS output driver has 8 drive strength settings (3 bits) and can also be independently enabled (logic high) or disabled (logic low) by writing into the corresponding bit, O1E for output 1 and O2E for output 2. An enabled output passes the generated output while a disabled output is in its tri-state condition (high impedance).

Please note that oscillator has to be already enabled via ENABLE pin prior to any serial programming. Please refer to the data sheet of the specific DSC21XX device for the typical rise/fall times for the different output strength settings.

Table 2-5 describes the output control register map. Register bits [7:4] are only applicable to dual output oscillators and can be ignored when programming a single-output oscillator.

TABLE 2-5: REGISTER MAP FOR CMOS OUTPUT DRIVE CONTROL

Register 7 6 5 4 3 2 1		0
0x11	O2S[2]	O2S[1]	O2S[0]	O2E	O1S[2]	O1S[1]	O1S[0]	O1E

2.3 HIBERNATE (LOW CURRENT) MODE

Using serial programming, the DSC21XX or DSC22XX devices can be put into a low current mode to save power. By programming the Hibernate bit (0x10<5>) to a high, the device will enter the low current mode. During Hibernate, all outputs are in the tri-state condition and the PLL and oscillator circuitry are powered down. Less than 100 A are consumed. Writing a 0 into the Hibernate bit (0x10<5>) will return the device to normal operation.

When writing to register-bit 0x10<5>, care must be taken to not modify the other bits in the register. This can be achieved by masking the other bits with their existing value when writing the hibernate command. The register should be initially read, then rewritten with bit<5> changed to the desired hibernate state while keeping other bits as is.

2.4 I ^2 C BUS CONTROL INTERFACE

The DSC21XX can be configured as a read/write slave device that conforms to Phillips I ^2 C bus specifications except a “general call”. The DSC21XX employs a three pin I ^2 C bus configuration. A Chip Select (Cs_bar) enables I ^2 C communications with DSC21XX. The I ^2 C bus transmits data and clock with SDA and SCL. SDA and SCL are open-drain, that is the device can only drive these lines low or leave them to float. The bus is controlled by a master device that generates the serial clock SCL, controls bus access and generates the START and STOP conditions while the DSC21XX works as a slave. When Cs_bar is low, the accessed device will respond to SDA and SCL. When Cs_bar is high, the accessed device will not respond to I2C signals. The I ^2 C slave interface follows the Philips Fast Mode (400 kHz) format.

The DSC21XX uses standard I2C data structures and timing sequences. Because the DSC21XX employs a three pin configuration where Cs_bar controls access to the device, any 7 bit slave address can be used in the read or write commands with the exception of all bits equal 0. Figure 2-1 displays the I²C timing diagram and specification.

SDA t_r sCL S t_HD;STA t_HD;DAT t_HIGH t_SU;STA s_r t_HD;STA t_SP t_P tBUF t_SU;STO P S MSC010

FIGURE 2-1: I ^2 C Timing Diagram.

TABLE 2-6: I ^2 C TIMING SPECIFICATION

Parameter Symbol Min Max Unit
SCL t	SCL	—	3	.
SET-UP Start t	SU_STA	160 ns
Hold Time Start t	HD_STA	160 ns
Low period SCK	tLOW	160 ns
High period SCK t	HIGH	160 ns
Data Set-Up Time	tSU_DAT	10		ns
Data Hold Time	tHD_DAT	0	70	ns
Rise Time: SCL	tCL	10	40	ns
Fall Time: SCL	tCL	10	40	ns
Rise Time: SDA	tDA	10	80	ns
Fall Time: SDA	tDA	10	80	ns
Set-Up Stop	tSU_STO	160	—	ns

The I ^2 C data format to perform read and write is as follows:

Master Controls SDA Line Slave Controls SDA Line Write to One Register in a Device Device (Slave) Address (7 bits) Register Address N (8 bits) Data Byte to Register N (8 bits) START R/W = 0 ACK ACK ACK STOP

FIGURE 2-2: I ^2 C Write To a (Slave) Register.

Read From One Register in a Device Device (Slave) Address (7 bits) Register Address N (8 bits) Device (Slave) Address (7 bits) Data Byte From Register N (8 bits) START R/W = 0 ACK Repeated START R/W = 1 ACK NACK STOP

FIGURE 2-3: I ^2 C Read From a (Slave) Register.

TABLE 2-7: COMMANDS TO CHANGE OUTPUT FREQUENCY

# Command Note/Comment
1 Set CS_low Very first command to issue		that will set CS_low
2	Write 0x0 into register 0x12	Reset register 0x12 to 0 in order to select frequency bank 0
3 Write N value to register 0x15 7 bits only,		bits7:1
4 Write F value into register 0x14 and bit0 of register 0x15		MSB of F value goes to bit0 of register 0x15Next 8 bits go to register 0x14Least 8 bits (7:0) are automatically truncated
5 Write M1 value into register 0x16 —
6 Write M2 value into register 0x17 —
7 Repeat 3-6 for each desired output frequency		—

2.5 SPI BUS CONTROL INTERFACE

The DSC22XX can be used as a read/write slave device that conforms to SPI bus link protocol. The DSC22XX employs the standard four pin SPI bus configuration. The SS (Chip Select) signal (Active Low) enables communications with DSC22XX. The bus transmits full duplex synchronous data over the MOSI (Master Out Slave In) and MISO (Master In Slave Out) pins. Data is clocked by SCLK. MISO can be tri-stated (high impedance) to permit multiple devices to share the bus.

The DSC22XX uses standard SPI data structures and timing sequences. SPI commands should be preceded by 4 idle/setup cycles with the SS pin held high. This should be followed by asserting SS (taking it low) and transmitting data on the MOSI pin MSB first. The first data consists of a 7-bit register address appended with a read/write selection bit in the LSB position (1=Read, 0=Write).

Figure 2-4 displays the SPI timing diagram and specification.

Clock Edge 0 1 tCH 2 3 tCL 4 5 6 7 CLK CS tCSHD tCH tCSWH DIN D0 D1 D2 D3 D4 D5 D6 D7 tDO DOUT D0 D1 D2 D3 D4 D5 D6 D7 (prev) (prev) (prev) (prev) (prev) (prev) (prev) (prev)

FIGURE 2-4: SPI Timing Diagram.

TABLE 2-8: SPI TIMING SPECIFICATION

Parameter Symbol	Min Max Unit
SCLK t	SCL	—	2	0
Low Period SCLK t	LOW	25 — ns
High Period SCLK	t_HIGH	25 — ns
DIN Set-Up Time	t_DS	10 — ns
DIN Hold Time	t_DH	0	—	ns
SCLK Fall to DOUT Valid	t_DO	—	2	2
SCLK High to CS High Hold	t_CSH1	22 — ns
SCLK High to CS Low Hold	t_CSH0	0	—	ns
CS Low to SCLK High Setup	t_CSS0	10 — ns
CS High to SCLK High Setup	t_CSS0	5	—	ns
CS Pulse Width High	t_CSS1	10 — ns

Figure 2-5 and Figure 2-6 displays example SPI communications.

SS SCLK MOSI A6-0 ADDRESS R=1 X - DON'T CARE X - DON'T CARE MISO D7-0 @ ADDRESS D7-0 @ ADDRESS +1

FIGURE 2-5: Example SPI Read Operation.

SS SCLK MOSI A6-0 ADDRESS W=0 D7-0 @ ADDRESS D7-0 @ ADDRESS + 1 MISO

FIGURE 2-6: Example SPI Write Operation.

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