ah, i'm about to build an icsp (well, it will actually power the 3 chip
circuit while programmng it before the end user puts the module to use).
 i wonder if rg174 coax for teh data and clock lines might not be a good
idea, as long as the cable isn't more than 2 feet or so long from the
programmers drivers.

this would add the capacitance but not the resistance but would prevent
cross talk as well (assuming the coax was grounded at the programer end
and the cable had seperate lines for the chips ground/power/vpp lines),
and i could also add a series drive resistance to cut down ringing in
the cable.

would the pic have trouble driving a little coax at moderate readback
speed?  thoughts?

it seems it would be cleaner and slicker to run coax to the micrograbers
i'll be using rather than a little board near the end (no room on this
project for an extra connector, the board is only 10mmX12mm and i have
chips on both sides, i'm just using wire test points for programming
line access placed where i could find a little space close to the chip pins).

Gerhard Fiedler wrote:
>
> > http://forum.microchip.com/tm.asp?m=39237
>
> > The little adapter looks like this:
> >
> > ICD2            Target PIC
> > <---------------> VPP
> > <---------------> VDD
> > <---------------> GND
> > <---- R --- C --> PGD
> > <-------- C ----> PGC
> >
> > R = 100 ohms
> > C = 22pf to GND
>
> Not sure it makes a lot of a difference, but Olin Lathrop writes in that
> thread:
>
> "The other part of the suggestion is to insert 100ohms in the PGD line
> between the 22pF cap to ground and the target PIC. The resistor and cap
> together form a low pass filter that attenuates the high frequencies of the
> edges when the target PIC is driving PGD. These high frequencies otherwise
> couple onto PGC and create spurious clocks seen only by the target PIC."
>
> If I understand that correctly, this would then be
>
> ICD2            Target PIC
> <---------------> VPP
> <---------------> VDD
> <---------------> GND
> <---- C --- R --> PGD  <<< R and C reversed
> <-------- C ----> PGC
>
> Gerhard
>
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