[sdiy] destroying flash memory cell on a PIC

Jay Schwichtenberg jschwich53 at comcast.net
Wed Mar 17 22:56:33 CET 2021


Another thing came to mind.

After the E/W cycle did you verify the memory that was written to FLASH?

Maybe the memory written (I assume RAM) got corrupted between setup and 
when it was written.

Jay S.

On 3/17/2021 11:50 AM, Jay Schwichtenberg wrote:
> 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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