[sdiy] destroying flash memory cell on a PIC

[cheater cheater]

Any chance you weren't wearing a wrist strap? :)

On Wed, Mar 17, 2021 at 11:59 AM Roman Sowa <modular at go2.pl> wrote:
>
> Hi,
> I was recently playing with PIC18 self-write and encountered strange
> problem. I can't be sure if it was because of my multiple write attempts
> (not that many of them) or it is extremely bad luck, but the
> microcontroller in question (PIC18F46K22) shows stange fault. About 20
> of flash memory bytes are showing 00 even if that range was not
> programmed. It is FF after bulk erase, but after programming even
> several kilobytes below, they read as 00.
> There's a pattern - they are all on 10-bit boundary, so it's address
> 400, 800, C00 and so on till FC00. To look even more strange, it's not
> all, but randomly few bytes fitting that pattern work OK.
> It happens either if I program it as self-write, or if using ICD3.
>
> Have anyone ever encountered this problem?
>
> After thousands of PICs used so far I have never encountered flash
> error. OTOH, I have never used self-write before, but despite looking
> like obvious coincidence I can't see a reason why self-write would
> damage a memory cell, or address decoder. Chip errata does not mention
> anything about memory precautions.
>
> Maybe I'm doing this too fast? The 64-byte page write is initiated just
> a couple of us after page erase is finished. This shouldn't be a problem
> but maybe worth trying to put 2-3ms delay.
> Thanks for your help!
>
> Roman
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