problem with TIMER1 when using internal LP oscillator

[bmoore]

I'm trying to run a simple program on my PICKit 2 44-pin Demo Board
(PIC16F887) that keeps track of the overflows on TIMER1 when it is
clocked by the internal 32kHz crystal (see C code below for the CCS
complier). The problem I'm having is that I only seem to get two
TIMER1 interrupt overflows instead of one every two seconds like I
expect. Code works fine if I set up TIMER1 to run off the main
processor clock (8MHz).

#include <16F887.h>

#use delay(clock=8MHZ)

#FUSES HS,INTRC,NOWDT,NOPUT,NOMCLR,NOPROTECT,NOCPD,NOBROWNOUT,NOIESO,NOFCMEN,NOLVP

int count; //keep track of TIMER1 overflows

#int_TIMER1
void TIMER1_isr(void)
{
count++; //increment count
output_d(count); //display count on LEDs

}

void main()
{
setup_timer_1(T1_EXTERNAL|T1_CLK_OUT); //use low power 32kHz crystal
(i.e. T1CON=0x8F)
enable_interrupts(INT_TIMER1);
enable_interrupts(global);
count=0xFF; // turn on all LEDs to start
output_d(count);
while(1);
}

[PCM programmer]

[Ttelmah]

Ignoring anything else, you cannot have both HS, and INTRC fuses. INTRC, is for the internal RC oscillator, HS, implies an external crystal, or oscillator....

Best Wishes

[bmoore]

[PCM programmer]

[bmoore]

[PCM programmer]

Look at the block diagrams for the main oscillators and for Timer1
in the data sheet.

Timer1 can be clocked by:
1. An external 32.768 KHz watch crystal, using the T1OSC.
2. An external clock input pin, T1CKI.
3. The main instruction cycle clock, Fosc/4.

There is no option to separately run Timer1 from the internal 31 KHz
oscillator, while running the main PIC at 8 MHz. So you can't do it.

[bmoore]