I am using a PIC16F887 as a controller for a laboratory process.

TMR1 is preloaded and allowed to timeout at 1sec a interval, the interrupt
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 power
up initialisation and startup is executed.

All works great....except....after some indeterminate period, varying from
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 would
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 cause
the microcomputer to resume operation

Any ideas would be much appriciated.

--=20
Perry Curling-Hope

Research and Development
--=20
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