Advanced Parallel I/O - The HCS12/9S12: An Introduction to Software and Hardware Interfacing - page 354

Example 7.9
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Suppose that the pins PP3..PP0 are used to drive the four transistors as shown in
Figure 7.41. Write a subroutine to rotate the stepper motor clockwise one cycle using the
half-step sequence.
Solution: The assembly language subroutine is as follows:
#include “c:\miniIDE\hcs12.inc”

step1 equ $08

step2 equ $0C

step3 equ $04

step4 equ $06

step5 equ $02

step6 equ $03

step7 equ $01

step8 equ $09

HStep movb #$FF,DDRP ; configure PTP for output

movb #step1,PTP

bsr delay10ms

movb #step2,PTP

bsr delay10ms

movb #step3,PTP

bsr delay10ms

movb #step4,PTP

bsr delay10ms

movb #step5,PTP

bsr delay10ms

movb #step6,PTP

bsr delay10ms

movb #step7,PTP

bsr delay10ms

movb #step8,PTP

bsr delay10ms

rts
; the following subroutine waits for 10 ms
delay10ms movb

#$90,TSCR1 ; enable TCNT and fast flags clear

movb #$06,TSCR2 ; configure the prescale factor to 64

bset TIOS,IOS0 ; enable OC0

ldd TCNT

addd #3750 ; start an output compare operation

std TC0 ; with 10-ms time delay

brclr TFLG1,$01,*

rts

end

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