Cirrus Logic AN88 - Manual

1
Copyright  Cirrus Logic, Inc. 1997
(All Rights Reserved)
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
AN88
Application Note
Interfacing the CS5525/6/9 to the PIC16F84
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 the Microchip PIC16
microcontroller series. This note takes the reader
through a simple example describing how to com-
municate with the ADC. All algorithms discussed
are included in the Appendix at the end of this
note.
ADC DIGITAL INTERFACE
The CS5525/6/9 interfaces to the PIC16F84
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 Port A (RA) on the PIC16F84 with a four-
wire interface, the algorithms can be easily modi-
fied 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 PIC16F84 to the ADC.
SDO, Serial Data Out, is the data signal used to
transfer output data from the ADC to the
PIC16F84.
SOFTWARE DESCRIPTION
This note presents algorithms to initialize the
PIC16F84 and the CS5525/6/9, perform a self-off-
set calibration, modify the CS5525/6/9 gain regis-
ter, and then acquire a conversion. Figure 2 depicts
CS5525/6/9 PIC16F84
RA0
RA1
RA2
RA3
CS
SDI
SDO
SCLK
Figure 1. 3-Wire and 4-Wire Interfaces
CS5525/6/9 PIC16F84
NC (RA0)
RA1
RA2
RA3
CS
SDI
SDO
SCLK
NOV ‘97
AN88Rev2