PIC18F8920... RTCC as 16 bit timer

[Pogostik]

I have been trying to use Timer0 in an 18F8720 device as a 16-bit timer. I can get my code to work when it is configured as an 8-bit counter, but when I set it to 16-bits, no interrupts occur. Here is a code snippet of a modified version of EX_STWT.C example from CCS:
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#int_timer0 // This function is called every time
void clock_isr() { // the RTCC (timer0) overflows (255->0).
// For this program this is apx 76 times
if(--int_count==0) { // per second.
++seconds;
int_count = INTS_PER_SECOND;
}
}

void main (void)
{
BYTE start;

int_count = INTS_PER_SECOND;
set_timer0 (0);
setup_timer_0 (RTCC_INTERNAL | RTCC_DIV_256 | RTCC_8_BIT);
enable_interrupts(INT_TIMER0);
enable_interrupts(GLOBAL);

InitializeSystem();
do {
printf("Press any key to begin.\n\r");
getc();
start=seconds;
printf("Press any key to stop.\n\r");
getc();
printf("%u seconds.\n\r",seconds-start);
} while (TRUE);
}
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When the initialization line is as follows timer 0 interrupts are generated.

setup_timer_0 (RTCC_INTERNAL | RTCC_DIV_256 | RTCC_8_BIT);

When the RTCC_8_BIT option is eliminated, which should cause timer 0 to become 16-bit, timer0 interrupts do not occur.

setup_timer_0 (RTCC_INTERNAL | RTCC_DIV_256);

Anyone experienced this? Is there a work-around? Thanks.

[Pogostik]

In my header I meant to type 18F8720. I don't think the 18F8920 is available yet....

[Guest]

Did you wait enough time? Setting up timer0 to 16 bit in your case could means 256 seconds (cca. 4 minutes) instead of the original 1 second.

[Pogostik]

Are you saying... setting timer0 to 16 bits and initializing it to 0 would result in 65535 ticks before interrupt; whereas setting it to 8 bits would require only 256 ticks before interrupt? I think that may be it. Let me try it with those adjustments.

OK... it works fine now. Thanks for the tip...