Date   : Sun, 31 Aug 1997 10:06:48 +0100
From   : Mike Tomlinson <jasper@...>
Subject: Re: Sideways RAMs

In article <19970829.090932.61@...>, Chris Johns
<cmjohns@...> writes

>I can dig out where the wires go if you like (it means taking my BBC apart
>and looking :)) I think I put it in my second machine when I got a Watford
>ROM/RAM board a while back.

One wire will be the read/write line and a good point to pick it up is
pin 8 of ic77. (that's where all the RAM boards I've used have picked it
up, and my Watford ROM board uses it too for its onboard 16k battery-
backed sideways RAM.) 

I'm fairly sure, but not positive, you could do an 8k sideways RAM by
obtaining a 6264 static RAM chip, bending up the R/-W pin, connecting
that to p8 ic77 and plugging it into a spare ROM socket.

A 16k sideways RAM will need two 6264 chips plus a bit of logic on the
address lines to select the correct one, hence a gate or 2.  Or a 32k
chip could be used, with the extra address pin cut off and R/-W
connected to pin8 ic77 as above, but with the top 16k wasted.

>I also had a little 16k SideWays RAM which only had one wire. After pondering
>over circuit diagarams to find out what signal that was I managed to connect
>it to an electron with a bit of glue logic (a few gates).

Did you solder it over the OS ROM or something?

-- 
Mike Tomlinson
~@...[127.0.0.1]