Date   : Thu, 19 Mar 2009 23:37:08 +0000
From   : jgh@... (Jonathan Graham Harston)
Subject: Hardware questions

Richard Gellman wrote:
> The question is, if I implement some control logic somewhere in
> FCxx, is it permissable to use the whole of FDxx as a 256-byte page
> window, and implement my own paging register in FCxx ? Or is there
> some hard-wiring that already implements a paging register in FDFF
> and FCFF ?
 
You implement the paging register yourself.
 
&FCFF is b8-b15 of the external address
&FCFE is b16-b23 of the external address
&FCFD is b24-b31 of the external address
See http://mdfs.net/Docs/Comp/BBC/Hardware/FREDAddrs
and http://mdfs/net/Docs/Comp/BBC/Hardware/RAMCard
 
http://mdfs.net/Info/Comp/BBC/CUBE/BeebEx.gif shows how to build a
12-bit paging register giving access to 2^20 bytes of memory.
 
-- 
J.G.Harston - jgh@...                - mdfs.net/User/JGH
Youth has now fled. Their best years have been passed in the service
of the party. They are ageing and their ideals have also passed,
dispersed by the contrarities of daily struggles.