Date   : Tue, 15 Jun 1999 15:59:10 +0100 (BST)
From   : "Andrew Benham" <adsb@...>
Subject: Re: BBC 8271 commands

Looking at the BBC B circuit diagram and the Intel 8271 data sheet,
the address mapping is:

Read Status      write to  FE80
Write Command    read from FE80
Read Result      read from FE81
Write Parameter  write to  FE81
Write Reset      write to  FE82
Write Data       write to  FE84
Read Data        read from FE84

Because of the BBC address decoding, multiple addresses can be used
for each of the above. A full BBC B simulation should probably handle
these other addresses, just in case.

 Main Address    Other working addresses
   FE80           FE88,FE90,FE98
   FE81           FE89,FE91,FE99
   FE82           FE8A,FE92,FE9A
   FE84           FE85,FE86,FE87,FE8C,FE8D,FE8E,FE8F,
                  FE94,FE95,FE96,FE97,FE9C,FE9D,FE9E,FE9F


--
Andrew Benham   adsb@...               
Nortel Networks Plc, London Road, Harlow, Essex CM17 9NA, United Kingdom
Tel: +44 1279 402372    Fax: +44 1279 405746

I speak for myself, my views are not necessarily the views
of Nortel Networks or any other corporation.