Reprogramming an existing 0 bit to an existing 0 in Flash memory

[El-Mohr]

I am using NXP S32K148 and am trying to change one bit in a flash page from 1 to 0 without erasing the page. Problem is that this will require writing 0s on existing 0s in the same phrase, which according to the reference manual is not allowed as it overstresses the device.

My questions are:

1- Does "not allowed" mean I can't do it, like it wouldn't be performed by hardware or it's doable but not advised?

2- If it's doable, what does it mean to "overstress the device", or to what extent should I be concerned knowing that I will do that only once?

Thanks

[lukaszadrapa · Accepted solution]

Hi,

overstress is not the only thing to consider. Next important point is ECC. Each phrase has hidden ECC syndrome which is programmed to the flash at the same time as data. If you are going to overwrite the phrase, new ECC syndrome corresponding to new data is calculated and ECC is programmed again. And it may be necessary to change '0' in old ECC syndrome to '1' which doesn't work, of course. It can lead to single or multiple bit ECC error.

So, it is possible to overwrite non-erased phrase but it's not recommended. And because this was not characterized, we can't give you guarantees.

Regards,

Lukas