Andy Howard wrote:
.........
>I'm thinking of adding an ICSP socket to a future product for field upgrades
>so I'd be interested to hear if you find any gotchas when you come to play
>with it.
>

I talked with Jeff of melabs a few weeks ago about using the
EPIC programmer for ICSP, and the major gotcha he mentioned was
regarding the exact cktry tied to /MCLR pin on the PIC. You have
to make sure you can pull the pin high fast enough [goes to current
drive out of the programmer], and also that the programmer doesn't
affect Vcc by backfeeding thru the /MCLR ckt.

Apparently, on some marginal P/S designs, Vpp can pull up the Vcc
bus. Maybe low current regulators, whatever. I did try this and
found Vpp actually kicked up the output of a 7805 [1A v.reg] a
couple of tenths of a volt. Have to watch the size of the pullup
resistor on /MCLR - ie, not too low - if that is all you have
on the pin. If you put a cap there, then you may not be able to
pull the pin up fast enough.

best regards,
- Dan Michaels
Oricom Techonlogies
http://www.sni.net/~oricom
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