Helmut Forren wrote:
>
> I previously posted "Can In-Circuit verify PIC16C73A but can't Program".
>
> I have done some more research and found that the real situation is that
> I have to remove the crystal before in-circuit programming will work.
> Previously, with the crystal in, I was actually "reading", not
> "verifying",
> and the result of that read turned out to not quite match the desired
> program.  At first glance, using a pre-programmed dip processor plugged
> into a circuit and then read via in-circuit programming techniques, the
> program read back out appeared to be shifted from the correct program...
> as if some bytes were omitted or some address increments occured twice,
> or something else just slightly off like that.
>
> Having poked around some more, I have discovered that if I simply remove
> the crystal from the circuit, I can program, verify, and I believe
> everything
> else works too.
>
> Unfortunately, I don't WANT to have to remove the crystal in order to
> in-circuit program.  This just increases the labor cost whenever I want
> to do it, and I'm considering doing it in a quantity of thousands.
>

The pic uses one of the programing pins for the clock during programing

>
> Does anyone have any suggestion as to why I find I must remove the
> crystal?
>
> Does anyone have any suggestions as to what I might do in order to be
> able
> to simply "plug and program", without removing the crystal or performing
> any other
> board mods before attempting in-circuit programming?

Just a single dip switch in series with osc. in crystal lead
should do

Or a small (4K7) resistor  in series with the osc.in and short the
crystal
side of the resistor to ground, with a link on the programing plug
if you want to make it fully automatic

Either method should stop the clock for programing

--
Peter Cousens
email: peter@cousens.her.forthnet.gr
snailmail: Peter Cousens, karteros, Heraklion, Crete, 75100, Greece,
phone: + 3081 380534,    +3081 324450   voice/fax

After Bill Gates announced to the world that he was Microsoft,
his wife was asked to comment. She said that as his wife, she
had been the first to notice this problem