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IOC strange behavior

 
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IOC strange behavior
PostPosted: Thu Jul 30, 2009 3:15 am     Reply with quote
Hello,

Although my interrupt routine works, I don't understand it's behavior.

I need the interrupt-on-change at a certain Pin (RA4). I thought that only edges would cause the IOC to start and it only would happen once per one edge.

So, I have the following simple code:
Code:

#int_RA
   void ext_isr() {
      INT_CNT++;
   }

main(){

   EXT_INT_EDGE(H_TO_L);
   enable_interrupts(INT_RA4);
   enable_interrupts(GLOBAL);

   INT_CNT = 0;

   while (TRUE){
     //here is my code}
   }


What happens is, the counter INT_CNT increments as long as RA4 is LOW. Using a button, the longer it is pressed and pulls to GND, the higher is the number of my counter. I thought it would just count ONE for ONE edge (even the switch bounces, it just could be three or four, but it is thousands for a short pressing.
So, the only explanation could be, that it is not edge triggered but pulse triggered.

Regards

Dieter
Bulova



Joined: 30 Jul 2009
Posts: 2

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Further info
PostPosted: Thu Jul 30, 2009 4:46 am     Reply with quote
Hello,

sorry I forgot to mention:

Compiler:
CCS PCM C Compiler, Version 3.239

Microcontroller:
PIC12F683

Best regards

Dieter
Bulova



Joined: 30 Jul 2009
Posts: 2

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Solved
PostPosted: Thu Jul 30, 2009 5:15 am     Reply with quote
Hello,

I found the answer by myself. Like so often, the answer is written in the datasheet:

Quote:
... clears the interrupt by
a) Any read or write of GPIO. This will end the mismatch condition.
b) Clear the flag bit GPIF.

A mismatch condition will continue to set flag bit GPIF.


This also answers other questions of my code revisions, where the RA4 is read within the ISR and causes the interrupt to be stopped after its execution. And thus causes "normal" behavior.

Regards

Dieter
Ttelmah
Guest
PostPosted: Thu Jul 30, 2009 6:17 am     Reply with quote
A forum search would have found this.
The 'B' changed interrupt, is one of about three common interrupts, where there are hardware things that 'must' be done in the interrupt handler.
Serial receive - you must read the character.
Serial transmit - you must either write another character, or turn off the interrupt.
Port B receive - read the port.

Glad you found it from the data sheet.

Best Wishes
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