Date   : Fri, 20 Oct 2000 00:06:34 +0100
From   : "Gordon Jefferyes" <gjeffery@...>
Subject: BBC B+ shadow ram question?

Could somebody please try and explain to me when the B+ is in shadow ram
mode how does
the machine control which ram bank is going to be writen to and read
from by
the processor?

I can see the IC36 pin 17 gives VDUSEL output which makes the video
display
use the shadow
ram area. (pin 17 being controlled by writing to D7 at &FE34)

But what controls the IC36 pin 12 output to set CPUSEL, which select
which
ram bank the processor
will read or write to?

I am trying to add BBC B+ support to my BBC MESS emulator so any help
would
be greatly
recieved.

Thanks

GordonJ.