Date   : Fri, 25 Jul 2008 10:23:55 +0100
From   : Charlie.Robson@... (Charlie.Robson@...)
Subject: EEPROM writing in SW rom bank?

"Ian Wolstenholme" <bbcmailinglist@...> wrote on 25/07/2008 
09:56:33:

> I'm not sure if this would be possible, or at least, as straightforward 
as it
> might appear to sound.  Presumably if you could just plug an EPROM into
> an SROM socket and connect a lead between the write line and pin 8 IC77
> or similar, then there wouldn't have been much of a market for EPROM
> programmers.
> And also, I expect you'd find hundreds of user modified Beebs with 
apermanent
> connection made between the two points, and probably a ZIF socket in the
> ROM slot as well so that the user could programme his own EPROMs at 
will.

You are indeed correct - for EPROMS. I am using an *EEPROM* which, for the
uninitiated, are writable a _bit_ like RAM, in that you don't necessarily
need to use a programming voltage to cook the bits, plain 'ol 5v will do 
it.

You write to the chip as you would a RAM, taking into account any protocol
required to turn off any 'soft' write protection, and then wait until it
takes its requisite time to self-program. You can poll for write 
completion
in a number of ways, usually involving reading back the byte you've just
written until bits stop flipping in some manner or other.


C




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