Date   : Thu, 20 Oct 2005 00:57:21 +0100
From   : jgh@... (Jonathan Graham Harston)
Subject: Re: Dual Floppies On A Master

Jules Richardson <julesrichardsonuk@...> wrote:
> Jon Ripley wrote:
> > When using a cable with a twist you need to set both drives to be drive
> > one.
 
Bl**dy stupid PC manufacturers!!!!  "Our users are too stupid to
work out how to set a drive select switch, so we'll put a twist in
the cable and ensure all the drives are set to drive 1".
 
> Can the beeb address four drives, or just two? I honestly can't
 
Define "drive" :)
 
> remember. IIRC the 8271 *should* be capable of it, but I think you end
 
The shugart floppy disk interface standard has four drive select
lines, DS0, DS1, DS2 and DS3, so allowing up to four drives to be
selected. The 8271 controller has two internal drive select lines,
only allowing two drives to be selected with a single controller.
 
The 1770 has no drive select lines. The drive must be selected
with external hardware. The BBC and B+ only have two drive select
lines, DS0 and DS1. The Master has three drive select lines, DS0,
DS1 and DS2, allowing up to three drives to be selected. However,
nothing in the DFS or ADFS drive access code ever selects the
third drive. You would have to write your own disk system to
access a drive with DS2. You may also have to set a link on the
motherboard.
 
-- 
J.G.Harston - jgh@...                - mdfs.net/User/JGH
Jet Set Willy Resources - http://mdfs.net/Software/JSW