Forrest Christian wrote 2011-07-23 11:33:
> I've got a design which uses the second uart in the new PIC18f26K22...
> Which happens to share it's pins with PGD and PGC.   I designed the
> circuit so that the field wiring is isolated enough that the circuit
> still operates, and the PICkit2 is still able to drive the pins during
> programming.
>
> Unfortunately, it also appears that the PICKit2 doesn't tristate those
> lines when it's done with them.  Thus preventing proper operation of the
> circuit.   It's a big pain to connect and disconnect this each time it
> runs.   Especially when making lots of subtle coding changes and
> reprogramming the chip.
>
> I would expect that some of the programmers out there will tri-state
> these lines (or for that matter, switching them to inputs), effectively
> removing the programmer from the circuit when not in use.  But this
> feature doesn't seem to be widely advertised if it exists at all.
>
> So, the question for the list is:  What programmers, if any, are known
> to effectively 'drop out' of the circuit when they aren't programming.
> That is, it can be safely left attached even to circuits which reuse the
> RB6/RB7 pins in their own circuit.
>
> Thanks.
>
> -forrest
>

I don't know about all programmers, but I'd *expect* any decent
programmer to do that. I've been using the Wisp628/648 programmers
for long and they does that.

I see from the schematics in the PICkit2 manual that it has hardwired
4.7 Kohm resistors to GND. So the target curcuit has to be able to
handle that at least, if one want to have the PICkit2 connected.
True trisate drivers might have been better.
--=20
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