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'In-circuit PIC16C73A programming - Must remove cry'
1997\02\09@132603 by Helmut Forren

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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.

Please note that I am using a Pro Mate II with firmware version
03.21.01.
I have made an adapter plug to go from the programmers ZIF socket to a
header on my own board.  I did a bit of research first to make sure this
concept worked, and it does by using merely the 5 documented in-circuit
programming pins (GND, VDD, MCLR, RB6, RB7).  Note that this does NOT
include the two crystal pins, so my difficulties in-circuit programming
with the crystal inserted must be related to the crystal's being
connected
to the processor while trying to program the processor, as opposed to
being related to some direct interaction between the crystal and the
Pro Mate II programmer.

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?

Thanks very much,
Helmut Forren
spam_OUThelmutTakeThisOuTspamatlanta.com
770-448-9550

1997\02\09@173458 by peter

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Helmut Forren wrote:
{Quote hidden}

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: .....peterKILLspamspam@spam@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

1997\02\10@085711 by Martin J. Maney

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On Sun, 9 Feb 1997, Helmut Forren wrote:

> 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

This sounds like something I've heard but not <knock wood> seen.  The
problem is likely that MCLR doesn't rise quickly enough, and the PIC runs
an instruction or two - which increments the PC, which does double duty as
the programming mode address register, of course.  As I recall, there was
a report of this where the effect was so repeatable that the chips
appeared to program and verify correctly because the offset was always the
same, but of course the program didn't work since it was in the wrong
location.

You need either to make the programming hardware pull MCLR up within spec
- a very small number of microseconds - or to disable the oscillator
during programming, perhaps by shorting the input pin to ground?

Luck!

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