Cirrus Logic AN131 - Manual (Page 5)

AN131
AN131REV2 5
5. CONCLUSION
This application note presents an example of how
to interface the CS5521/22/23/24/28 to the
68HC05. It is divided into two main sections: hard-
ware and software. The hardware interface illus-
trates both three-wire and a four-wire interface.
The three-wire interface is SPI and Microwire™
compatible. The software section illustrates how to
initialize the converter and microcontroller, write
to the CSRs, write and read the ADC’s internal reg-
isters, perform calibrations, and acquire conver-
sions. The software is modularized and provides
important subroutines such as write_register,
read_register,
write_csrs and convert, which were
all written in 68HC05 assembly language.
The software described in the note is included in
Section 6. “APPENDIX: 68HC05 Microcode to In-
terface to the CS5521/22/23/24/28” on page 6.
Command Time
8 SCLKs
8 SCLKs Clear SDO Flag
Data SDO Continuous Conversion Read
SDO
SCLK
SDI
t *
d
Data Time
24 SCLKs
MSB LSB
* td = XIN/OWR clock cycles for each conversion except the
first conversion which will take XIN/OWR + 7 clock cycles
XIN/OWR
Clock Cycles
Figure 5. Conversion/Acquisition Cycle Timing
MSB High-Byte
Mid-Byte
Low-Byte
A) 24-Bit Conversion Data Word (CS5522/24/28)
MSB High-Byte
Mid-Byte
Low-Byte
B) 16-Bit Conversion Data Word (CS5521/23)
0- always zero, 1- always one,
CI1, CI0 - Channel Indicator Bits
OD - Oscillation Detect, OF - Overflow
Figure 6. Bit Representation/Storage in 68HC05
D23 D22 D21 D20 D19 D18 D17 D16
D15 D14 D13 D12 D11 D10 D9 D8
D7 D6 D5 D4 D3 D2 D1 D0
D15 D14 D13 D12 D11 D10 D9 D8
D7 D6 D5 D4 D3 D2 D1 D0
1 1 1 0 CI1 CI0 OD OF