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

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Dear all,
We faced with the same problem for 16F877 and it is solved by the following
change in DelayMs routine of interrupt.c (in firmware)

while((tick-lasttick)<(2*cnt))continue;

Since our hardware is not exactly the same hardware of usbpicprog (it is
compatible with gtp-usb lite and has a 12 Mhz xtal ), I thought that it was
only our problem. But after seeing last messages of Marcel and Marcelo I
want to share our solution.

Frans, you are saying that you have tried more delays in programming
sequence but I do not know the length of your additional delays and maybe
you can also try 2*cnt solution. You will notice but I should also indicate
that this change is unnecessarily affecting the programming times of all
PICs.

I should also note that while compiling the firmware with MPLAB we had to
comment out some part of the code in prog.c (related to the PICs we are not
planning to use), since it was not fitting into the program memory of
18F2550.

Kindest regards,
Fatih.

On Mon, Apr 11, 2011 at 5:38 PM, Marcelo Maggi <mm...@ho...> wrote:

>  Thank you Frans for your prompt reply.
>
> I fully agree that the noise comes from the USB power line, since I can see
> it even with the programmer disconnected. What I also noticed is that the
> mosfet is somehow amplifying the noise, that is the reason why I added a
> 100nF capacitor at the gate, besides the large one directly on the Vdd line
> after the mosfet. The large current as well as the time constant introduced
> by this capacitor were the concerns I had at the beginning, so I started
> testing with lower values until I reached 470 uF, which seems a good
> compromise between noise reduction and unwanted side effects.
>
> Unfortunately this is not a solution for the PIC16F877A... it keeps showing
> the erratic behavior I described in my previous message.
>
> I will appreciate if you could let me know if you find a solution in the
> future... I will keep experimenting from my side and let you know any
> progress.
>
> Thank you again.
>
> Best regards
>
> Marcelo Maggi
>
> ------------------------------
> Date: Mon, 11 Apr 2011 08:58:30 +0200
> From: fra...@gm...
> To: usb...@li...
> Subject: Re: [Usbpicprog-technical] Unstability when programing large
> pieces of code
>
>
> 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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