Date   : Tue, 10 Aug 2004 13:09:48 +0000
From   : Jules Richardson <julesrichardsonuk@...>
Subject: Re: ROM Burning

On Tue, 2004-08-10 at 12:12, Chris Priest wrote:

> I have a selection of 27C256 roms OTP version, I thought I would be
> able to use these, but although it burns OK, the rom is not
> recognised.

> Do I need to offset the data by anything before burning?  Or is it not
> possible to use 256=E2=80=99s in a beeb? The rom image is only 8k.


Ok, looking at the schematic for the beeb, 27256 devices should work,
but you can only use the top half (16KB) as address line A14 (pin 27) is
tied to +5V (this is /PGM on 27128 and 2764 devices). The bottom 16KB
will always be ignored.

Also, jumpers S32 and S33 dictate whether address line A13 of the ROMs
is tied to A13 on the beeb's address bus, or whether it's always tied to
+5V. S32 controls ROMs in sockets IC52 and IC88, whilst S32 controls
ROMs in IC100 and IC101. In the 'west' position A13 is controlled by the
machine's address bus, in the 'east' position, A13 is always at +5V.

by the way, www.bbcdocs.com and www.acornmanuals.co.uk are both good
resources for scans of BBC-related documentation, assuming you don't
have relevant user guides etc. already.

cheers,

Jules