Cirrus-logic AN131 Instrukcja Użytkownika Pobierz 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

AN131

Application Note

Interfacing the CS5521/22/23/24/28 to the 68HC05

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 Acquiring Conversions ...................................... 4

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

5. CONCLUSION ....................................................... 5

6. APPENDIX: 68HC05 MICROCODE TO INTERFACE

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

1. INTRODUCTION

This application note details the interface of Cirrus

Logic’s Crystal

CS5521/22/23/24/28 Analog-to-

Digital Converter (ADC) to a Motorola 68HC05

microcontroller. This note takes the reader through

a simple example describing how to communicate

with the ADC. All algorithms discussed are includ-

ed in Section 6. “APPENDIX: 68HC05 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 68HC05

through either a three-wire or a four-wire interface.

Figure 1 depicts the interface between the two de-

vices. Though this software was written to inter-

face to the three-wire SPI

on the 68HC05, the

algorithms can be easily modified to work in the

four-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 68HC05 to the ADC.

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

transfer output data from the ADC to the 68HC05.

CS5521/22/23/24/28

68HC05

PA0

MOSI (PD3)

MISO (PD2)

SCK (PD4)

SDI

SDO

SCLK

Figure 1. 3-Wire and 4-Wire Interfaces

CS5521/22/23/24/28 68HC05

No Connect

MOSI (PD3)

MISO (PD2)

SCK (PD4)

SDI

SDO

SCLK

3-Wire Interface 4-Wire Interface

NOV ‘99

AN131REV2

1 2 3 4 5 6 ... 13 14

Podsumowanie treści

Strona 1 - Application Note

Strona 2 - 3.1 Initialize

AN13110 AN131REV2;*****************************************************************************;* Routine - convert ;* Input - none;* Output - convers

Strona 3 - 3.4 Read/Write Gain Register

AN131AN131REV2 11JSR send_spi ;Transfer low byteRTS ;Return;*****************************************************************************;* Routine -

Strona 4 - 4. MAXIMUM SCLK RATE

AN13112 AN131REV2;* Routine - delay;* Input - count in ACCA;* Output - none;* This routine delays by using the count specified in ACCA. The 68HC05;*

Strona 5 - 5. CONCLUSION

• Notes •

Strona 6

Strona 7

AN1312 AN131REV23. SOFTWARE DESCRIPTIONThis note presents algorithms to initialize the68HC05 and the CS5521/22/23/24/28, modify theCS5521/22/23/24/28

Strona 8

AN131AN131REV2 3ing the number of Setups to be accessed and sub-tracting 1. Because each CSR holds two Setups,this number must always be an odd value,

Strona 9

AN1314 AN131REV23.5 Acquiring ConversionsTo acquire a conversion the subroutine convert iscalled. For single conversions on one physicalchannel, the

Strona 10

AN131AN131REV2 55. CONCLUSIONThis application note presents an example of howto interface the CS5521/22/23/24/28 to the68HC05. It is divided into two

Strona 11

AN1316 AN131REV26. APPENDIX: 68HC05 MICROCODE TO INTERFACE TO THE CS5521/22/23/24/28;****************************************************************

Strona 12

AN131AN131REV2 7MAIN EQU * ;Start from reset vector;*** Initialize and Calibrate the system ***JSR initialize ;Initialize the SystemJSR write_csrs ;Mo

Strona 13 - • Notes •

AN1318 AN131REV2BNE sloop ;Repeat loop if counter isn’t zeroLDA #%11111110 ;Load ACCA with last byteJSR send_spi ;Send final byte to ADCRTS ;Exit rout

Strona 14

AN131AN131REV2 9; Setup 4 Settings - (A1-A0 = 00, Physical Channel = 3, OWR = 15Hz,; input V-range = 25mV, Unipolar)LDA #$4C ;Load ACCA with first byt

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