> Well, um, yeah.  Note that PGC and PGD are always held low
> unless Vdd is up
> and stable.  This means there is no chance of parasitic SCR
> latchup.  But
> yes, there will be some current thru the protection diode of
> the target chip
> when being run at a low Vdd level.

Note that there will also be protection diode current through your
progger-PIC when you run the target at 6.0 Volt (max for a 16C84), or
are you running the progger PIC at 5.5 and limiting the Vhigh to 5.5?

This different-Vcc issue is one of the things that kept me from
designing a production-grade version of Wisp628.

In the older WISP I solved this by running the progger-PIC at the same
voltage as the target. In those days the 16C84 was the only target, and
the progger-PIC was of course a 16C84. This approach did have some funny
interaction with Vcc-dependent Vpp generator :(

Wouter van Ooijen

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Van Ooijen Technische Informatica: www.voti.nl
consultancy, development, PICmicro products

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