Date   : Fri, 12 Nov 2010 18:19:51 +0100
From   : rick@... (Rick Murray)
Subject: ROMs

On 12/11/2010 14:56, Ben Collier wrote:

> I was wondering if anyone could tell me which sorts of chips will work
> as ROMs in the BBC ROM slots.

Traditional EPROMs of the following types:
   27256  16K
   27128  32K

A 27512 (64K) might work?

Those can be either traditional (as given) or CMOS (beginning 27C...).


> Are there commercially available chips of one sort or another which will
> fit and are easily programmable?

You ought to be able to find a supplier of these, however in this day 
and age you might need to buy in quantity rather than "a couple".

Do you have a dump nearby, or a shop flogging off old kit? You might 
find EPROMs in old kit, but it'll be a bit hit'n'miss.

Programming? Sorry. It needs an EPROM programmer, and if erasing is 
required you'll need to cook it under a UV lamp. It is pretty 
straightforward, but it is slow and faffy.


If you were hoping for an in-situ Flash to reprogram, you can get little 
Flash devices in a ROM style pinout (such as the AMD 28F256 in PDIP), 
but the question remains - how do you get the data onto it in the first 
place? You can, with the Am28F256 part, program them in a standard EPROM 
programmer [*], which is cool, but in this respect it doesn't offer much 
over a traditional EPROM, save for the lack of UV erasure.


Best wishes,

Rick.


* - note, looking at the datasheet, it looks as if a special command
     needs to be sent to invoke erasure; which means that many
     traditional EPROM programmers may not work unless their software
     or firmware can be modified to do this...

-- 
Rick Murray, eeePC901 & ADSL WiFI'd into it, all ETLAs!
BBC B: DNFS, 2 x 5.25" floppies, EPROM prog, Acorn TTX
E01S FileStore, A3000/A5000/RiscPC/various PCs/blahblah...