[En-Nut-Discussion] UROM file system and RAM vs Flash allocation on AT91SAM

[Harald Kipp]

Nathan Moore wrote:

> None of them allow you to skip the page erase if you are only clearing
> some bits, such
> as appending data to a partially used page?

As far as I understood, NOR Flash generally allows to program each
byte/word for exactly one time after an erasure cycle. There had been
devices, which explicitly offered to reprogram a byte/word a limited
number of times without erasure, to clear the remaining bits. I assume,
that this is still possible with today's flash chips, but no longer
mentioned in the datasheets. Definitely the reliability suffers (reduced
data retention time).

The reason for not being able to modify single bits is, that the
internal buffer is several bits long and the whole buffer must be used
for a single programming cycle. On parallel NOR flash devices, the
buffer is at least 1 byte. On serial flash chips it is 1 page.

Harald