Cirrus-logic AN130 Manual de usuario descargar pdf

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Cirrus Logic, Inc. 1999

P.O. Box 17847, Austin, Texas 78760

(512) 445 7222 FAX: (512) 445 7581

http://www.cirrus.com

AN130

Application Note

Interfacing the CS5521/22/23/24/28 to the PIC16C84

TABLE OF CONTENTS

1. INTRODUCTION ................................................... 1

2. ADC DIGITAL INTERFACE ................................... 1

3. SOFTWARE DESCRIPTION ................................. 2

3.1 Initialize ............................................................. 2

3.2 Write Channel Setup Registers ........................ 2

3.3 Self-Offset Calibration ....................................... 3

3.4 Read/Write Gain Register ................................. 3

3.5 Acquire Conversion .......................................... 4

4. MAXIMUM SCLK RATE ......................................... 4

5. SERIAL PERIPHERAL INTERFACE ..................... 4

6. DEVELOPMENT TOOL DESCRIPTION ................ 5

7. CONCLUSION ....................................................... 5

8. APPENDIX: PIC16C84 MICROCODE TO

INTERFACE TO THE CS5521/22/23/24/28 .......... 6

1. INTRODUCTION

This application note details the interface of Crys-

tal Semiconductor’s CS5521/22/23/24/28 Analog-

to-Digital Converter (ADC) to the Microchip

PIC16C84 microcontroller. This note takes the

reader through a simple example which demon-

strates how to communicate between the microcon-

troller and the ADC. All algorithms discussed are

included in Section 8. “APPENDIX: PIC16C84

Microcode to Interface to the

CS5521/22/23/24/28” on page 6.

2. ADC DIGITAL INTERFACE

The CS5521/22/23/24/28 interfaces to the

PIC16C84 through either a three-wire or a four-

wire interface. Figure 1 depicts the interface be-

tween the two devices. Though this software was

written to interface to Port A (RA) on the

PIC16C84 with a four-wire interface, the algo-

rithms can be easily modified to work with the

three-wire format.

The ADC’s serial port consists of four control

lines: CS, SCLK, SDI, and SDO.

CS, Chip Select, is the control line which enables

access to the serial port.

SCLK, Serial Clock, is the bit-clock which controls

the shifting of data to or from the ADC’s serial

port.

SDI, Serial Data In, is the data signal used to trans-

fer data from the PIC16C84 to the ADC.

SDO, Serial Data Out, is the data signal used to

transfer output data from the ADC to the

PIC16C84.

CS5521/22/23/24/28

PIC16C84

RA0

RA1

RA2

RA3

SDI

SDO

SCLK

Figure 1. 3-Wire and 4-Wire Interfaces

CS5521/22/23/24/28

PIC16C84

RA1

RA2

RA3

SDI

SDO

SCLK

3-Wire Interface 4-Wire Interface

NC (RA0)

NOV ‘99

AN130REV2

1 2 3 4 5 6 ... 15 16

Indice de contenidos

Pagina 1 - Application Note

Pagina 2 - 3.1 Initialize

AN13010 AN130REV2MOVLW 0x05 ; Command to write CSRsBCF PORTA, CS ; select the ADCCALL send_byte ; send command byte to ADC;*** Setup CSR #1 - Setups 1

Pagina 3 - 3.4 Read/Write Gain Register

AN130AN130REV2 11;* Routine - convert;* Input - none;* Output - 24-bit Conversion Results in memory locations HIGHBYTE, MIDBYTE;* and LOWBYTE

Pagina 4 - 4. MAXIMUM SCLK RATE

AN13012 AN130REV2;* Routine - write_register;* Input - COMMAND, HIGHBYTE, MIDBYTE, LOWBYTE;* Output - none;* This subroutine writes to the internal re

Pagina 5 - 6. DEVELOPMENT TOOL

AN130AN130REV2 13;* Routine - send_byte;* Input - Byte stored in W register;* Output - none;* This subroutine sends a byte, one bit at a time, MSB fir

Pagina 6

AN13014 AN130REV2;* Routine - delay;* Input - Count in W register;* Output - none;* This subroutine delays by using a count value stored in register W

Pagina 7

• Notes •

Pagina 8 - BCF PORTA, CS ; Enable ADC

Pagina 9

AN1302 AN130REV23. SOFTWARE DESCRIPTIONThis note presents algorithms to initialize thePIC16C84 and the CS5521/22/23/24/28, performcalibrations, modif

Pagina 10

AN130AN130REV2 3DP0 must always be logic 1 when reading and writ-ing the CSRs. To modify the Depth Pointer bits, theconfiguration register is read to

Pagina 11

AN1304 AN130REV23.5 Acquire ConversionTo acquire a conversion the subroutine convert iscalled. For single conversions on one physicalchannel, the MC

Pagina 12

AN130AN130REV2 5for a selectable clock polarity. However, many donot have the capability to select the clock’s phase.When using a microcontroller with

Pagina 13

AN1306 AN130REV28. APPENDIX: PIC16C84 MICROCODE TO INTERFACE TO THE CS5521/22/23/24/28;**************************************************************

Pagina 14

AN130AN130REV2 7;* Routine - main;* Input - none;* Output - none;* This is the entry point to the program, as well as the central loop. ;*************

Pagina 15 - • Notes •

AN1308 AN130REV2MOVLW 0xFF ; Load W for new delay countCALL delay ; Delay for Oscillator start-up 158msCALL delay ; Delay for Oscillator start-up 158m

Pagina 16

AN130AN130REV2 9;* Input - none;* Output - none;* This subroutine writes to and reads from the gain register on physical;* channel 1.;****************

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