Tony Matthews wrote:
>
> Adolfo Cobo (Ingenieria Fotonica) wrote:
> >  Hello to all,
> >  I need to program a 16c84 part soldered to the PCB, and I've built two
> > homemade programmers: a "ludipipo" for the serial port and a "topic" for
> > the parallel port.
> >  None of them are able to program the pic in the circuit, but they work
> > fine with a "off-circuit" PIC.  I've read in this List some things to try:
> >
> >    - Stop the PIC oscillator grounding the OSC1 pin.
> >    - Shield the cables to the PIC.
> >    - Cables as short as possible.
> >
> >  My questions is: It's really needed to stop the PIC oscillator? What else
> > can I try?
> >  Thanks in advance.
> >
> I had to isolate the programming pins with a switch even though the
> circuits the pins were connected to were relatively high in impedance I
> suspect rise time problems due to capacitive loading.Afterwords it
> occured to me that I probably could have built a cmos buffer into a dip
> clip and succeded but I did'nt try it.There's no doubt others on the
> list with more usable advice but I just could'nt help myself..Tony M.

I used what I call a bulldozer approach. This requires a 4PDT switch and
target board that is suitably designed to accept a programming cable.
I/We also are programming SimmSticks with 84's in circuit. Again the
target SimmStick
is isolated from other hardware with the 4PDT switch, and a suitably
designed programmer.

If you can design your target board to suit, this principle works a
treat.
There are many piclisters using this method. Isn't that right guys?

Take a look at:
http://www.dontronics.com/84.html
for the circuit used. This may help.

BTW SimmSticks can be seen at:
http://www.dontronics.com/sstudio.html
and many new boards are being announced.
http://dontronics.com/new.html

PS BTW More info on Picstart and Newfound programmer firmware upgrades
can be
seen at:
http://dontronics.com/phoenix.html


Don McKenzie  don@dontronics.com   http://www.dontronics.com

PICSTART and Newfound PIC Programmers Firmware Upgrades.
SLI, the serial LCD that auto detects baud rates from 100 to 125K bps.
SimmStick(tm) A PIC proto PCB the size of a 30 pin Simm Memory Module.
Send a blank message to help@dontronics.com for more info.