At 01:38 PM 10/03/97 -0500, you wrote:
>Hey, all, I know this was already a discussion, but it was never answered
>to my satisfaction...  I have a PIC based card here that doesn't go
>absolutely to 0 VDC when power is off... the PIC always screws up...  Can
>someone PLEASE suggest a simple-reliable solution?  Can microchip put a
>GND-shorting switch in their parts?

You could use a reset device by Maxim to force the CPU to stay in a
reset state if the applied voltage is low. That would be the most reliable
solution - I think there are some very small surface mount devices that
can do this. This will also ensure that the next power up reset is clean.

Is the PIC device you are using specified to operate at lower voltages, if
so then detect this with a spare I/O pin and make it do nothing etc.

Its not practical to change a device design and a GND short could cause all
sorts of problems.

Have you tried something as simple as a pulldown resistor on your PIC voltage
pin ? You might not need a small value if the voltage is close to that at
which the device will not run at all.

Just how much current is there anyway to allow your PIC to operate when
the power is off ?

Rgds

Mike
Perth, Western Australia

Some say there is no magic but, all things begin with thought then it becomes
academic, then some poor slob works out a practical way to implement all that
theory, this is called Engineering - for most people another form of magic.
                                                                       Massen