Problem selecting external crystal as clock source

pallavaggarwal — Wed, 21 Jun 2006 15:27:57 GMT

hi,

I want to run my controller QB8 using external crystal 4.9152MHz

and not using internal

i have used the following code as atest but after removing thr crystal also i get the pulses on PTB0 .

please check my code and guide me how to use the external cystal as clock

source

this program just makes on/off PTB0

#include <hidef.h> /* for EnableInterrupts macro */
#include <MC68HC908QB8.h> /* include peripheral declarations */

//macro defination for BIT wise manupulation
#define setbit(A,B) A|=(1<<B)
#define clrbit(A,B) A&=~(1<<B)

void main(void)
{

unsigned char a=0,i=0;

OSCSC=0xC4;
CONFIG1=0x01;//Disable COP
DDRA=0x10;
DDRB=0xFF;

while(1)
{
PTB=0x01;
for(i=0;i<100;i++);
PTB=0x00;
for(i=0;i<100;i++);
}
}

Re: Problem selecting external crystal as clock source

peg — Wed, 21 Jun 2006 17:41:39 GMT

Hi pallav,

It appears to me that you should write 0xC4 to OSCSC.

Then wait about 1ms to stabilise.

Then set ECGON in OSCSC.

Then shortly after you should be running on ext xtal.

Refer to 11.3.2.2 of QB8 datasheet.

Regards David