Hi Olin
I was fairly certain there wasn't a rise time issue because I do a lot of RF
boards where I use that same stackup so I have a good feel for the amount of
capacitance of a trace to GND.

So after reading your message I tried erasing the device with the ICD2
before attempting to program this morning and presto the device programmed
verified and works in the circuit just fine using the pro_prog.

It also spoke/responded to the programmer at -VDD 5v or when I entered
pic_prog at the command line when erased.

I started the 47pF cap experiment a few days ago but only managed to get it
on the PGD line and I was distracted before I could finish and I never got
around to trying it on both lines.

If you look at the plots I sent the PDG has a much slower rise time than the
PGC line because it has the 47pF still soldered on. (I meant to remove it
before doing the rise time test but spaced it off)
I added the 47pF to the PGC line but the device still doesn't want to talk
unless it is first erased by the ICD2.
If it is blank then things seem to work just fine whether at 5 or 3 volts.

What should I try next?

Phillip
Things should be as simple as possible but no simpler
 
 
 
Phillip Coiner
CTO, GPS Source, Inc.
 
 
Your source for quality GNSS Networking Solutions and Design Services, Now!
-----Original Message-----
From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On Behalf Of
Olin Lathrop
Sent: Friday, April 13, 2007 6:48 AM
To: Microcontroller discussion list - Public.
Subject: Re: [PIC] Pro_programer/head in dark place troubles

Phillip Coiner wrote:
> CH1=VPP
> CH2=PGD
> CH3=PGC
> CH4=VDD

The rise and fall times look to be within range.  Everything looks OK for 3V
operation.  The edges all look fast enough and the data line is well settled
by the falling edge of the clock line.

>> The command was pic_prog -VDD 3 -HEX t
>> (If I use -VDD 5 the device won't talk at all.)

So that means it can communicate at 3V, but of course won't program
correctly since it can't do a bulk erase.

This is smelling more and more like a crosstalk problem.  Have you tried
putting 47pF or so caps on PGC and PGD on your board as I suggested several
messages ago?

> What should I try/measure next?

Try the things I suggested to address a crosstalk problem and see what that
does.  If that doesn't fix it I'm out of ideas.  All I can suggest then is
to send the unit back for a refund, or send me one of your boards and let me
look into it on my bench.


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