Date   : Tue, 27 May 2003 01:08:50 +0100
From   : tom@...
Subject: Re: B+ shadow RAM query

If VDUSEL sets the high bit of video addresses, I think the way I'm 
doing it is correct. If you set the CRTC registers suitably under the 
emulator, you would see the 12K of paged RAM at the bottom of the 
shadow memory. 

Still on the subject of the B+, I'm having an odd problem: *FX200,3 
followed by BREAK causes the computer to reset into mode 3, try to 
boot the disc, then hang in what I guess is the B+ equivalent of this 
bit in OS 1.20:

       DC59    LDA     &0267   ;if BIT 0 set and DISC EXEC error
       DC5C    ROR             ;occurs
       DC5D    BCS     &DC5D   ;hang up machine!!!!

Ctrl+BREAK gets things back to normal. It's as if *FX200 is changing 
the keyboard link settings. Sure enough *FX200,255 causes no 
problems.

On the B of course *FX200,3 disables ESCaPE and sets the OS to clear 
memory on reset. Did this _really_ change for the B+?! I'm sure loads 
of stuff used it. Or is something wrong?

--Tom