The SPI Function - The HCS12/9S12: An Introduction to Software and Hardware Interfacing - page 503

Solution: The procedure for generating the specified waveform is as follows:
Step 1
Configure SPI0 module properly.
Step 2
Output a high (5 V) from V OUTA and also output a high from V OUTB .
Step 3
Wait for 1 ms.
Step 4
Output a low from V OUTB .
Step 5
Wait for 1 ms.
Step 6
Output a low from V OUTA and output a high from V OUTB .
Step 7
Wait for 1 ms.
Step 8
Output a low from V OUTB .
Step 9
Wait for 1 ms.
Step 10
Go to step 2.
The value to be sent to MCP4922 to output a high from V OUTA is 0x3FFF whereas the value
to be sent to generate a low from the V OUTA pin is 0x3000.
The value to be sent to MCP4922 to output a high from V OUTB is 0xBFFF whereas the value
to be sent to generate a low from the V OUTB pin is 0xB000.
The assembly program for generating the specified waveform is as follows:
#include “c:\miniide\hcs12.inc”

org $1500

lds #$1500 ; set up the stack pointer

jsr openSPI ; configure the SPI0

bset DDRK,BIT7 ; configure PK7 pin for output

forever ldd #$3FFF ; output a high from V OUTA

jsr sendMCP4922 ; “

ldd #$BFFF ; output a high from V OUTB

jsr sendMCP4922 ; “

ldy #1 ; wait for 1 ms

jsr delayby1ms ; “

ldd #$B000

jsr sendMCP4922

ldy #1

jsr delayby1ms

ldd #$3000

jsr sendMCP4922

ldd #$BFFF

jsr sendMCP4922

ldy #1