[sdiy] a provoking question about time

Roman Sowa modular at go2.pl
Fri Jun 24 15:47:51 CEST 2022

Noone wants to touch the "fuse" settings.
But then again, if this is the same kind of flash as rest of memory, and 
not any "high endurance" or whatever, with 10 times bigger transistors, 
then it's really dead end.

But do we have to erase it at all? It is to be rweritten with the same 
value so no need for erasing config bytes. I haven't planned to erase 
anything in the program memory either, just write the same content to 
pump up the charge in flash cells.


W dniu 2022-06-24 o 14:50, mskala at northcoastsynthesis.com pisze:
> On Thu, 23 Jun 2022, Roman Sowa wrote:
>> I've seen corrupted memory in products made about 15 years ago with dsPIC, so
>> datasheet value seems real.
>> One way to do it is to rewrite all memory from time to time, but how to do
>> that? Even if there's real time clock running, the user may always change the
> The last page of flash program memory on the PIC24F parts I'm using cannot
> be rewritten under program control because it contains the configuration
> "fuse" settings.  Erase it as a first step in rewriting it, and you've
> bricked the part.  The only safe way to program it is through in-circuit
> programming with a separate programming device, not practical to implement
> as part of a product.  So one basically just has to accept that the
> lifetime of data in that page, and therefore of the part because that data
> is essential for boot-up, will be the lifetime of the initial programming.
> Now, my understanding is that the configuration "fuses" are read to
> separate registers upon boot-up rather than being used directly from
> program memory.  So it seems plausible that maybe one could erase the last
> page, have the microcontroller continue running, and then rewrite the page
> and it would be okay, provided the entire operation happened without any
> interruption of power.  But I haven't attempted that and it's certainly
> not authorized by Microchip - their docs say never try to rewrite the last
> page under program control at all.  It would be very fragile with respect
> to to any power interruption during the attempt.

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