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Cirrus Logic, Inc. 1997

Cirrus Logic, Inc.

Crystal Semiconductor Products Division

P.O. Box 17847, Austin, Texas 78760

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

http://www.crystal.com

AN89

Application Note

Interfacing the CS5525/6/9 to the 68HC05

By Keith Coffey

INTRODUCTION

This application note details the interface of Crys-

tal Semiconductor’s CS5525/6/9 Analog-to-Digi-

tal 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 the Appendix at the end of this note.

ADC DIGITAL INTERFACE

The CS5525/6/9 interfaces to the 68HC05 through

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

1 depicts the interface between the two devices.

Though this software was written to interface to the

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.

, 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.

SOFTWARE DESCRIPTION

This note presents algorithms to initialize the

68HC05 and the CS5525/6/9, perform a self-offset

calibration, modify the CS5525/6/9’s gain register,

and acquire a conversion. Figure 2 depicts a block

CS5525/6/9 68HC05

PA0

MOSI (PD3)

MISO (PD2)

SCK (PD4)

SDI

SDO

SCLK

Figure 1. 3-Wire and 4-Wire Interfaces

CS5525/6/9 68HC05

No Connect

MOSI (PD3)

MISO (PD2)

SCK(PD4)

SDI

SDO

SCLK

NOV ‘97

AN89Rev2

1 2 3 4 5 6 ... 11 12

Indice de contenidos

Pagina 1 - Application Note

Pagina 2 - 2 AN89Rev2

AN8910 AN89Rev2*************************************************************************************** Routine - delay* Input - Count in register

Pagina 3 - AN89Rev2 3

• Notes •

Pagina 4 - MAXIMUM SCLK RATE

Pagina 5 - APPENDIX

AN892 AN89Rev2diagram. While reading this application note,please refer to the Appendix for the code listing.InitializeInitialize is a subroutine that

Pagina 6

AN89AN89Rev2 3information from the CS5525/6/9 to the 68HC05via the SPITM. Similar to send_spi, receive_spi re-ceives a byte one bit at a time MSB firs

Pagina 7

AN894 AN89Rev2.MSB High-ByteMid-ByteLow-ByteA) 20-Bit Conversion Data WordMSB High-ByteMid-ByteLow-ByteB) 16-Bit Conversion Data Word 0- always zero,

Pagina 8

AN89AN89Rev2 5APPENDIX68HC05 Microcode to Interface to the CS5525/6/9****************************************************************************** Fi

Pagina 9

AN896 AN89Rev2*************************************************************************************** Program Code******************************

Pagina 10

AN89AN89Rev2 7*************************************************************************************** Subroutines*******************************

Pagina 11 - • Notes •

AN898 AN89Rev2*************************************************************************************** Routine - convert* Input - none* Output -

Pagina 12

AN89AN89Rev2 9*************************************************************************************** Routine - read_register* Input - COMMANDBYTE

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