PIC16F877A Comparator interrupt always triggered

[lloydi12345]

Hi, my program about comparator interrupt has a problem. Can you help me with this one? The circuit below is a battery low voltage indicator. I think ISR is activated but it is always triggered. In my program, portb.f0's state should be inverted as soon as the voltage CMCON.C1OUT state is changed. Can you check my program? Here's my code:

void interrupt(void){
     PORTB.F0 = ~PORTB.F0;   //invert the output on portb pin 0
     PIR2.CMIF = 0;
}

void main() {
     TRISA = 0XFF;
     TRISB = 0x00;
     PORTB = 0x00;
     CMCON = 0b00000011; //Use external voltage reference connected to RA3
                         //"-" input of C1 connected to RA0
                         //Mode 011

     PIE2.CMIE = 1;
     INTCON.PEIE = 1;
     INTCON.GIE = 1;
     
     while(1){}
}

I attached my schematic below. I hope you can help me.

 

[ericgibbs]

hi,
Check your CMCON settings.

 

[Pommie]

You have both comparators enabled. The other comparator will be oscillating and causing the interrupt.

Mike.

 

[lloydi12345]

Thanks for the reply ericgibbs and Pommie, I changed my mode from 011 to 001. It is still triggered.

 

[lloydi12345]

Hi, I changed my code with this one. I think it is not anymore triggered. But can you double check my code please? I'm not so sure if I'm able to disable it.

void interrupt(void){
     CMCON.C2OUT = 0;
     PORTB.F0 = ~PORTB.F0;
     PIR2.CMIF = 0;
}

Is this one alright?

 

[Pommie]

That should work. Even though CMCON.C2OUT is read only, any read or write to CMCON will clear the interrupt condition.

Mike.

 

[lloydi12345]

That should work. Even though CMCON.C2OUT is read only, any read or write to CMCON will clear the interrupt condition.

Mike.

great! thanks to both of you