Re: Atmel Dataflash (AT45DB642) anyone experienced stuck bits?



Rob Horton wrote:
I have been using the 8MB, AT45DB642, from Atmel for a number of years
now. It has become apparent that some of the chips we use have stuck
bits at various locations. So far this has exhibited itself in two
forms.
(1) a consistent pattern that occurs through every one of the 8192
pages.
(2) a random scattering throughout a portion of the memory.

Anyone experienced something like this or are my sources of chips
coming from the "gray market"?

Random bit errors can have several causes.

If you write too many times to the dataflash you will see bits which
fails to erase.

There is a soft limitation here.
The device is divided into blocks of 256 pages, and after
sending 10,000 erase commands to a block, either to a single
page or to a set of pages, any memory in the block
not erased starts to become unreliable.
If you make sure that each page in a block is erased
during such a cycle, you do not see a problem.
This limitation is described in the datasheet, and
only affects the AT45DB642 (which is obsolete) and does
not affect the new AT45DB642D.

If you have brownout, then the CPU can do anything
including writing random data to dataflash.

The AT45DB642 has a long hold time requirement.
I believe that not all Linux Drivers will honour that hold time.

If you have a buggy SPI, then this may cause the problem.
Check the errata of the MCU you are using to make sure
that this is not the issue.

Having a consistent pattern in everyone of the 8192 pages
in my opinion indicates a H/W error in the read circuitry.
Could be ESD related.

--
Best Regards,
Ulf Samuelsson
ulf@xxxxxxxxxxxxx
This message is intended to be my own personal view and it
may or may not be shared by my employer Atmel Nordic AB



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