Re: [Usbpicprog-technical] Unstability when programing large pieces of code

[Frans S. <fra...@gm...>]

Dear Marcelo Maggi,

I have indeed noticed this behaviour before, but not for all pic
devices. It seems to happen only on some revisions of pics and it is
very unpredictable. It also depends on the computer you are using it on.
I have been trying to add more delays in the programming sequence, but
that also didn't seem to help much. At least it is good to hear that
there is a solution for the behaviour for the 628A.
The funny thing is that the +5V is directly obtained from the usb power
line of the computer and is only switched by one mosfet. The noise seems
to come from the usb port in most of the cases. Also on the programmer,
the +5V is stabilized with 4x 100nF and one time 100nF after the mosfet
directly on the VDD pin of the output port. A 470uF capacitor could do
the job but also introduces a large current while switching the VDD pin
on (there is no current limiter) but if it works, there is no problem!

Kind regards,

Frans Schreuder

On 04/11/2011 04:48 AM, Marcelo Maggi wrote:
> Dear Frans:
>
> Thank you for this excellent programmer; I built it and I am currently
> running the latest beta version (0.4.2), both firmware and software
> (AMD64 version).
>
> I have been through a few issues; while I solved some of them, I need
> your support with one.
>
> First thing I noticed was that I had trouble when trying to program
> the PIF16F628A using more than half of the program memory. The
> programming cycle goes OK, but  during the verify step there were
> problems reported (byte read different from what was expected). It
> used to happen at different parts of the code, and eventually I could
> have a few successful attempts. Trying to find the cause of the
> problem, I noticed that Vdd (5 volts) was very noisy; I added a large
> capacitor (470 uF/16v) between Vdd and GND at the connector to the ZIF
> board (P1), and a 0.1 uF at the gate of Q3 (BS250). With Vdd now much
> cleaner, I can program the PIC16F628A with no problem each and every
> time. This may help reply the question from another user in this forum
> (posted on April 10).
>
> Now, I am trying to program larger PICs... I tried with the
> PIC16F877A, filling almost all of the program memory. Now, I have the
> same problem again; while verifying there are errors at different
> points of the program each time, with a few successful attempts.
> Further stabilization of Vdd does not help. What I noticed is that
> only a small portion of the program is corrupted when it fails to
> verify. It may happen at different parts of the code each time, but
> the wrong sequence is always the same:
>
> FF 3F FF 3F FF 3F FF 3F FF 3F FF 3F FF 3F FF 3F 00 00 00 00 00 00 00
> 00 00 00 00 00 00 00 00 00
>
> After this sequence, the program continues with the right code.
>
> Have you experienced this before? Any clue of what could be the reason
> with the information given?
>
> Just for your reference, the same happens with the latest stable
> version 0.4.1.
>
> Thank you in advance for your ideas...
>
> Best regards
>
> Marcelo Maggi
>
>
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