MEASURE THE PERIOD OF A SIGNAL

[Juan Pablo]

I am working with a PIC16F877 and a oscilator of 20 MHz.

I need to measure the period of a square wave every 0.5 seconds, so I try to use the RTCC (76 interruptions per second, which I have to use in the programme) and enable the CCP1 interruption every 0.5 seconds, disabling it when the period is obtained:

...
set_rtcc(0);
setup_counters(RTCC_INTERNAL, RTCC_DIV_256);
enable_interrupts(INT_RTCC);
setup_ccp1(CCP_CAPTURE_RE);
setup_timer_1(T1_INTERNAL|T1_DIV_BY_4);
enable_interrupts(GLOBAL);
...
#int_ccp1 void velocidad() {
long peraux;
disable_interrupts(GLOBAL);
if(!segundo){
//first rising edge
subida1 = CCP_1;
segundo=1;
}
else{
//second rising edge
subida2 = CCP_1;
peraux = subida2 - subida1;
segundo=0;
//Global int variables
auxi=peraux;
valor=peraux>>8;
}
disable_interrupts(INT_CCP1);
enable_interrupts(GLOBAL);
}

The period is obtained correctly but the PIC resets itself in 5 or 6 minutes time.

I didn´t use Watchdog, the stack used 4 of its 8 positions, RAM is used at 72 % (worst case) and ROM at 23 %.

Does anybody know why it happens? I can say that if I don´t enable CCP1 the PIC works properly.

Any better idea to implement this application?

Thanks in advance.

[Guest]

I know something that happened: your CAPS LOCK was inadvertently activated during the typing of the topic title...

[Mark]

Don't monkey around with the interrupt enable inside of the int. Ints are automatically enabled/disabled. You are enabling the int during and int. If another int occurs, you are going to trash the temp storage.

[Juan Pablo]

I have placed the next code in main function:

...
if(activar){
enable_interrupts(INT_CCP1);
activar=0;
}
else{
if(convertir){
disable_interrupts(INT_CCP1);
convertir=0;
}
}
...

And it seems that the problem has disappeared.

Thanks for your help!!!!