Sounds like the classic floating input problem.  Check the=20
initialization, pull up, pull down state of all pins.

Joe W


On 1/25/2013 11:45 AM, Perry Curling-Hope wrote:
> I am using a PIC16F887 as a controller for a laboratory process.
>
> TMR1 is preloaded and allowed to timeout at 1sec a interval, the interrup=
t
> service routine then determines if the interrupt was caused by TMR1, and
> decrements a register containing a time countdown value, prompting the
> process to advance when the register reaches zero.
>
> The Watchdog period is slightly greater than 1 second, (to accomodate the
> rest of the code execution loop) and the watchdog is cleared within the
> interrupt service routine ( a watchdog light is toggled there as well)
> On an occurrence of a reset, the timeout in STATUS register bit4 is
> examined to determine if the reset was caused by the WDT, and the program
> redirected to resume execution in the correct place, else the normal powe=
r
> up initialisation and startup is executed.
>
> All works great....except....after some indeterminate period, varying fro=
m
> a couple of minutes to over 3 hours, the watchdog light stops and the LCD
> displaying the time countdown  'freezes', indicating that the micro has
> ceased executing the loop.
> One would expect that if the watchdog was not being serviced, a reset wou=
ld
> ensue regardless and the machine would resume execution...somewhere.
>
> Not so....it appears 'dead', as if the LFINTOSC has ceased, which is not
> supposed to happen.
> Even a 'hard' reset applied to the MCLR/Vpp pin (which is enabled and
> effects an immidiate reset at all other times) does not restart the micro=
'.
>
> Only a complete power down and restart through powering up again will cau=
se
> the microcomputer to resume operation
>
> Any ideas would be much appriciated.
>

--=20
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist
.