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

[Marcelo M. <mm...@ho...>]

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