On Thu, 20 Mar 1997 14:11:39 +0200 Corne Smith
<csmith@WPSMTP.AVITRONICS.CO.ZA> writes:
>Hi dudes
>
>I've got a basic question that I still don't understand.
>
>What is the wachdog timer used for ?
>I know it is used to reset the PIC,but why ?
>
>Cheers
>
>Corne
>


        I think it's because ALL computers will crash, it's just a
question of how long it will be until they crash.  The watchdog timer
detects the crash and resets the system.  This compares favorably to a
system I put in Kansas ten years or so ago where I had to drive over 100
miles to press the reset at a remote FM transmitter site.  Now,
EVERYHTING I do includes a watchdog!
        Another post asked why the watchdog kept resetting his PIC even
though he had CLRWDT in his code.  It IS important that the CLRWDT be
executed BEFORE the WDT times out.  It's pretty common to put a CLRWDT at
ONE PLACE in the main program loop so if the processor doesn't make it
around to there at least every so often, we assume the thing crashed and
reset it.  If the main loop has a smaller loop inside it that keeps the
main loop from being completed in time, you can get a WDT timeout.  I had
this happen because of loops I put in to allow for A/D settling time.
        Finally, CLRWDT should NOT be put in an interrupt service routine
since sometimes the main program can crash, but interrupts keep running
fine.


Harold