Date   : Sat, 26 Aug 2006 10:02:22 +1000
From   : "Bob Devries" <bdevries@...>
Subject: Re: writing and reading on 3.5 floppy

The pinout from a PC floppy controller use the following connections:
Pin 10: Motoron drive A
Pin 12: Drive Select Drive B
Pin 14: Drive Select Drive A
Pin 16: Motoron Drive B

The disk drive is wired as follows:
Pin 10: Drive select 0
Pin 12: Drive select 1
Pin 14: Drive select 2
Pin 16: Motoron

All PC disk drives are set for drive 1.
The twist in the cable causes the signal from pin 10 to go to pin 16 of the 
drive on the end of the cable (drive A) and pin 14 goes to pin 12 . Pin 12 
goes to 14 (which has no connection on the drive, and pin 16 goes to pin 10 
which also has no connection on the drive.

It was done this way so that any idiot user could install a second disk 
drive without doing anything to the drive.

The BBC computer (and others) must have a cable without a twist, and must 
use a drive for drive 0 that can be jumpered for drive 0. Newer 3.5" drives 
do not have any jumpers, and are permanently wired for drive 1. Some still 
have soldered jumpers that can be modified, though.

Hope it helps.

--
Regards, Bob Devries, Dalby, Queensland, Australia

Isaiah 50:4 The sovereign Lord has given me
the capacity to be his spokesman,
so that I know how to help the weary.

website: http://www.home.gil.com.au/~bdevasl
my blog: http://bdevries.invigorated.org/

----- Original Message ----- 
From: "Pete Turnbull" <pete@...                >
To: <bbc-micro@...         >
Sent: Saturday, August 26, 2006 7:11 AM
Subject: Re: [BBC-Micro] Re: writing and reading on 3.5 floppy


> On Aug 25 2006, 12:07, Mike Howard wrote:
>
>> I'm no expert on the workings of floppys & drive selection. I believe
>> though, that the twist in a PC cable forces the drive to drive 0
> (zero)
>> from drive 1 (default). Therefore, connecting a floppy connector to
> the
>> end of a twin BBC cable (no need to remove the BBC flat edge
> connector)
>> leaves the 3.5" drive as drive one (as there is no twist in the BBC
> cable).
>
> Actually the twist causes the drive to behave as drive 1 instead of
> drive 2, not 1 instead of 0.  Therefore a drive set up for a PC,.
> connected on the end of the cable beyond the twist, will appear as
> drive 1; that is to say it would respond to DS1 (DRIVE SELECT 1) on the
> interface, not DS0 (nor DS2, or DS3).  If the drive selects on the
> drive were not altered, but it were moved to before the twist, it would
> appear as drive 2, ie it would respond to DS2.  That's no use to a
> Beeb, though, because a Beeb only uses DS0 and DS1 -- "drive 2" and
> "drive 3" in DFS are simply the other sides (the upper surfaces) of
> drives 0 and 1, and have nothing to do with what any other system might
> call drives 2 and 3.
>
> The twist actually doesn't swap one drive select line into the place of
> another.  In fact it swaps drives selects with motor control lines, one
> of which is entirely a figment of IBM's imagination, so it's even worse
> than it seems.
>
> Clear as mud?  Take a look at the interface specs, especially the
> *original* before IBM screwed it up for PCs.  For example, try reading
> Michael Haardt's handy "Floppy User Guide", from about page 12 on.
>
>
> -- 
> Pete Peter Turnbull
> Network Manager
> University of York
>
>
>
> -- 
> No virus found in this incoming message.
> Checked by AVG Free Edition.
> Version: 7.1.405 / Virus Database: 268.11.6/427 - Release Date: 24/08/2006
>
>