I have a 16C77A based monitoring system that utilizes the analog input
channels. 4 of the channels are connected to temperature sensing devices
that operate on 12 VDC and generate a 1-5 volt analog signal for 32-100
degrees.

When the temperature sensing devices are connected with power on,
occaisionally the processor locks up. We're seeing a 7 volt spike
occaisonally when the devices are plugged in, but no postive proof that
this is locking the processor up.

The watchdog timer is enabled and should reset the processor as the
routines that kick the dog do not appear to be working (reception of serial
input data or timer interrupts). The unit does not respond to the host,
indicating that the serial i/f is not working and an activity LED no longer
flashes, possibly indicating that the PIC is no longer processing
interrupts or is out in left field.

Can an overvoltage condition on the analog input cause the processor to
head for left field?

Howard
Howard McGinnis
hmcginni@digital.net
Electronic Visions, Inc.
1650 Barrett Drive
Rockledge FL 32955
(407) 632-7530
http://ddi.digital.net/~hmcginni
mcginnis@e-visions.com