[sdiy] destroying flash memory cell on a PIC

[Jay Schwichtenberg]

I've used some PIC16s, PIC18s, PIC24s and PIC32s without any problems.

Looking at the datasheet there is 10K min E/W speced so shouldn't have a 
problem.

Did you look for an Errata sheet for the chip and see if there are any 
issues noted (always do this if you get weird behavior)?

I've worn out ARM FLASH before but it took a while.

Jay S.

On 3/17/2021 3:55 AM, Roman Sowa 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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