Date   : Sat, 12 Jun 1999 09:31:54 +0100
From   : Stuart William McConnachie <stuart@...>
Subject: Re: BBC 8271 commands

In message <3.0.5.32.19990611164707.0092e510@...>, Michael
Foot <mikef@...> writes
>I'm wanting to know exactly how the BBC controlled the disc via the 8271
>chip so I can emulate it properly. Can anyone fill in or correct the
>locations in the memory map below?

>FE80 read status register, write command
>FE81 read result register, write parameter
>FE82
>FE83
>FE84 read/write data register
>FE85
>FE86

AFAIAA the missing locations do nothing at all.  I've certainly never
seen any BBC DFS access them, and pcBBC simply returns &FF as a read of
these locations and totally ignores writes.  I seem to recall the 8271
may have been capable of some type of DMA access to memory?  Of course
the BBC hardware does not support this, so it would be fairly pointless
emulating it anyway.

Regards,
-- 
Stuart McConnachie (stuart@...              )
43 The Hollows, Long Eaton, Nottingham, NG10 2ES, UK
Mobile: 0966 224307