Timer Functions - The HCS12/9S12: An Introduction to Software and Hardware Interfacing - page 381

movb #$04,TCTL1 ; change pin action to toggle
clr HIorLO ; LoCnt will be the delay count next time
bra $ ; prepare to perform other operations
; *********************************************************************************
; OC5 interrupt service routine starts a new OC5 operation with delay count equal to
; HiCnt or LoCnt depending on whether HIorLO flag is 1 or 0. After starting a new OC5
; operation, toggle HIorLO flag.
; *********************************************************************************
OC5ISR

tst HIorLO ; which delay count should be added?

beq addLow ; if 0 then select LoCnt

ldd TC5 ; select HiCnt as the delay count for

addd #HiCnt ; the new OC5 operation

std TC5 ; “

clr HIorLO ; toggle HIorLo flag

rti

addLow ldd TC5 ; select LoCnt as the delay count for

addd #LoCnt ; the new OC5 operation

std TC5 ; “

movb #1,HIorLO ; toggle HIorLO flag

rti
end
The C language version of the program is as follows:
#include “c:\cwHCS12\include\hcs12.h”
#define HiCnt 1200
#define LoCnt 1800
char HiorLo;
void main (void)
{

TSCR1

5 0x90;

// enable TCNT and fast timer flag clear

TSCR2

5 0x03;

// disable TCNT interrupt, set prescaler to 8

TIOS | 5 OC5; // enable OC5 function

TCTL1

5 0x0C;

// set OC5 action to pull high

TFLG1

5 0xFF;

// clear all CxF flags

TC5

5 TCNT 1 10;

while(TFLG1 & C5F); // wait until C5F is set

TCTL1

5 0x04;

// set OC5 pin action to toggle

TC5

15 HiCnt;

// start an new OC5 operation

HiorLo

5 0;

// add LoCnt for the next OC5 operation

TIE

5 0x20;

// enable OC5 interrupt locally

asm(“cli”); // enable interrupt globally

while(1);

}
interrupt void oc5ISR (void)
{

if(HiorLo){

TC5

15 HiCnt;

HiorLo

5 0;

}