Todd Peterson <PICLIST@MITVMA.MIT.EDU> wrote:

> >PIC16C74. If the power supply is momentarily shorted
> >(milliseconds), the PIC does not recover, but locks up in random
> >modes. We have the Watchdog timer ON and CLRWDT is only given one
> >time in the main program loop. Any ideas?
>
> if the program counter (instruction pointer) is being loaded with
> garbage that is outside your program loop, the watchdog timer
> should fire and reset the PIC unless the clock/oscillator has
> stopped.

Todd:

Wrong on both counts:

1.  If the PIC's Vdd line drops below the operational threshold (3V
or so), but DOESN"T fall below 0.7V, the PIC will latch up when
power is restored, and the watchdog timer will NOT reset it.

2.  Under normal circumstances, the watchdog timer works EVEN IF the
clock is stopped.

-Andy

Andrew Warren - fastfwd@ix.netcom.com
Fast Forward Engineering, Vista, California
http://www.geocities.com/SiliconValley/2499