Date   : Sun, 25 May 2003 19:05:33 +0100
From   : tom@...
Subject: B+ shadow RAM query

I'm adding B+ support to my emulator. On a B+, which RAM does the 
video output come from? If I switch to shadow RAM, does what's on the 
screen change, or does the memory as the CPU (apart from the VDU 
drivers area, that is) see it?

The B+ service manual is a bit unclear. It sort-of implies that video 
output comes from shadow RAM, so switching shadow RAM on leaves 
memory seemingly unchanged, but a different display is produced.

At the moment I'm assuming this is how it works. However, this is 
surely contrary to how shadow RAM addon boards worked on a real Beeb, 
because the 6845 can't get at the memory on the new circuit board?

The B+ shadow RAM currently seems to work fine; I'd like it to be as 
accurate as possible though! Any information appreciated. Thanks.

-- 
--Tom