Date   : Sat, 10 Jul 2010 19:47:48 +0100
From   : jgh@... (J.G.Harston)
Subject: Homemade SW-RAM

walker_matt wrote:
> I have 2 6264 chips (8kbit * 8) lying around, does anyone have any circuit
> diagrams for a 16KB sideways ram board I can make with few other components

Solder one 8K ram on top of another, except for the A13 lines.
Glue a 74LS04 inverter on top.
Wire the +ve and GND lines of the 74LS04 to the +ve and GND lines of
the RAM
Wire from the A13 line of the bottom RAM (the pin that will be plugged
into the socket) to the input of an inverter, wire the output of the
inverter to the top A13 - this selects between the two halves of the
16K bank to select the correct 8K RAM.
Connect a flying lead from the WE line on the two RAMs and connect
to IC76p7 to collect the Write signal.

> Another point, would 16KB more be any use? The B+ had 32KB more, with 20KB
> as shaddow RAM I think.

If you have some 32K RAMs lying around it's a bit easier, and it gives
you 32K SRAM! see http://mdfs.net/Info/Comp/BBC/SROMs/32K

> One more thing, how would I make use of the sideways RAM?

You need *SRLOAD (and maybe *SRSAVE) commands - see
http://mdfs.net/Mirror/Image/JGH/JGH-018.ssd and
http://mdfs.net/Mirror/Archive/JGH/Utility2.zip

JGH