Cirrus Logic AN130 - Manual (Page 5)

AN130
AN130REV2 5
for a selectable clock polarity. However, many do
not have the capability to select the clock’s phase.
When using a microcontroller with both features,
the clock polarity should be set to idle low, and the
clock phase should be set to begin clocking in the
middle of the data bits. For an SPI port without the
variable clock phase feature to function properly
with the CS5521/22/23/24/28, the clock polarity
needs to be set to idle high, and the ADC’s serial
port must be re-initialized anytime new informa-
tion is transmitted between the microcontroller and
the converter.
6. DEVELOPMENT TOOL
DESCRIPTION
The code in this application note was developed
with MPLAB
TM , a development package from Mi-
crochip, Inc. It was written in Microchip assembly
and compiled with the MPASM
TM assembler.
7. CONCLUSION
This application note presents an example of how
to interface the CS5521/22/23/24/28 to the
PIC16C84. It is divided into two main sections:
hardware and software. The hardware section illus-
trates both a three-wire and a four-wire interface.
The three-wire interface is SPI™ and MICROW-
IRE™ compatible. The software, developed using
tools from Microchip, Inc., illustrates how to ini-
tialize the converter and microcontroller, write to
the CSRs, write and read the ADC’s internal regis-
ters, perform calibrations, and acquire conversions.
The software is modularized and provides impor-
tant subroutines such as write_register,
read_register,
write_csrs and convert, which were
all written in PIC assembly language.
The software described in the note is included in
Section 8. “APPENDIX: PIC16C84 Microcode to
Interface 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-ByteLSB
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 1
CI1, CI0 - Channel Indicator Bits
OD - Oscillation Detect, OF - Overflow
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
Figure 6. Bit Representation/Storage in the PIC16C84