/* Generate a square wave at the PA6 output pin using OC2

Can change the variable half_cyc_delay in main as desired */

#code 0xC000

#data 0xD000

#include <startup.c>

#include <68hc11.h>

#include <stdio.h>

 

#define REG_BASE 0x1000

int half_cyc_delay;

int temp; /* used by interrupt service routine since service routine cannot have local variable */

 

/***************************************

* Service routine: schedule next toggle for OC2 

****************************************/

interrupt toc2(){

     temp = peek(REG_BASE+TOC2); /* get delay time for 1/2 cycle*/

     temp = temp + half_cyc_delay; /* add to last compare value */

     poke(REG_BASE + TOC2,temp); /* schedule next edge */

     bit_set(REG_BASE + TFLG1, 0x40);

} 

/***************************/

initialize(){

     pokeb(REG_BASE+TCTL1,0x40); /* OM2:OL2 = 0:1 -> OC2 toggle */

     pokeb(REG_BASE+TFLG1,0x40); /* clear OC2 flag */

     pokeb(REG_BASE+TMSK1,0x40); /* enable OC2 */

}

/***************************/

main(){

half_cyc_delay = 10000;

poke(0xDD,toc2); /* store toc2 address into pseudo interrupt vector+1 */

initialize();

e_int(); 

while(1) ;

}