Date   : Thu, 24 Jul 2008 16:13:48 +0100 (WET-DST)
From   : PCOGHLAN@... (Peter Coghlan)
Subject: EEPROM writing in SW rom bank?

>
>I'm trying to write an EEPROM by connecting a flying lead from the /WE
>line as one would for a RAM chip. Needless to say it's not working for
>me else I wouldn't be asking for help here :)
>
>Has anyone attempted to do anything like this with any degree of
>success or am I barking up the wrong tree? Or just barking?
>
>I'm sure the parameters of the chip - an atmel 28c64 - are compatible
>with what I'm trying to achieve, but it resolutely refuses to program.
>
>I'm using a standard BBC B.
>
>All help greatly appreciated
>

Hi Charlie,

I looked into doing this for (part of) an AT28C256 and found (for reasons
that I have now forgotten) that it was not straightforward.

It could have been something like OE being in the wrong state or CE not
asserted for long enough, the address bus not being stable for long
enough or something else entirely.

I decided that the way to proceed was to modify my eprom programmer to
do the writing, and then never got around to finishing the job...

As far as I recall, the data sheet for the AT28C256 said it could be
programmed one byte at a time or in "page mode" (64 bytes at a time).
Selection of page mode was determined by writing the subsequent bytes
quickly enough after the first one. If you weren't quick enough, it
went off in a huff to program the first byte for a considerable time
before becoming ready to accept another byte. This would probably
manifest as the first byte getting written, followed by a big gap
followed by a byte written much further along etc etc. Of course the
28c64 could be completely different...

Regards,
Peter.