Date   : Thu, 27 Mar 2003 12:05:34 +0000
From   : jgh@... (Jonathan Graham Harston)
Subject: Re: Sideways RAM

Kate Kneebone <kate.kneebone@...> wrote:
> a mere computer scientist!), I reckon I need to:
> 
> o buy a 62256 static RAM chip, which seem to be really cheap, so that's OK.
> o stick it in a ROM socket on my chosen computer.
> o bend up the A14 pin (1) and connect this up to an unused output of
> IC76 (pin 11 or 12), disconnecting the diode it's connected to, so I can
> address all my 32K.
> o bend up the RnW pin (27) and connect this to the computer's RnW line
 
That's what I've done in some of my Beebs. The only difference is that I
put the RAM in a 28-pin DIL socket and bend its pins to get the A14 and
RnW lines. I then plug the RAM into the socket, and plug the socket into
the socket on the motherboard.
 
I usually get RnW from IC77 pin 8 where it is sync'd with the CPU clock,
and connect A14 to ROMSEL bit 3 at IC76 pin 11. The diodes are usually not
fitted, and you may not need to disconnect them. The ROMSEL bit 3 toggles
the ROM bank by 8, so this puts the RAM in bank 4/12, 5/13, 6/14 or 7/15
depending on which of the four sockets you plug it into.
 
> clip the other end of the wires onto IC legs with the squeezy, hooky
> things you get on logic analysers (assuming you can buy these somewhere,
 
That's what I do. You should be able to get them at about 20p each.
 
-- 
J.G.Harston (JGH BBC PD Library) 70 Camm Street, Walkley, SHEFFIELD S6 3TR
jgh@...                - Running on BBCs & Masters with SJ MDFS FileServer
Z80+6502/CoPro+Tubes/Econet+SJ - - - - - - - http://www.mdfs.net/User/JGH/