Date   : Sat, 13 Nov 2010 19:57:44 +0100
From   : rick@... (Rick Murray)
Subject: ROMs

On 13/11/2010 11:12, Pete Turnbull wrote:

> Except that a Beeb can only access 16KB in the ROM sockets, and
> therefore uses 8KB 2764 or and 16KB 27128 EPROMs.  If you use a 27256 or
> bigger, you can still only access 16K (and may need to do some tricks to
> make that reliable).

True. I have a dual EPROM with different teletext images. Which is 
selected depends upon whether the flying lead soldered to the high 
address pin is hooked to +v or 0v.

It's a useful "hack". ;-)

Likewise, I *think* the DNFS is plain DFS and DNFS? I recall building up 
that EPROM but I don't know if I fitted it.

Perhaps with junk like that around, I ought to build some sort of 
memory-addressed latch so selecting which image to use is a matter of 
typing a command and hitting Ctrl-Break.


Best wishes,

Rick.

-- 
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...