Date   : Tue, 25 Oct 2005 01:04:27 +0100
From   : Richard Gellman <splodge@...>
Subject: Re: Collected notes on floppy drive butchery?

Pete Turnbull wrote:

>On Oct 24 2005, 10:10, Richard Gellman wrote:
>
>  
>
>>To clarify on the twist/untwist scenario:
>>
>>    
>>
>Er, no.
>
I'm starting to think you just want to make me look like I'm talking out 
of my a***.

Now, I have the Shugart floppy cable pinout in front of me right now, 
and I can see the following:

Pin 10 - Motor Enable A
Pin 12 - Drive Select B
Pin 14 - Drive Select A
Pin 16 - Motor Enable B

Now, unless there's some kind of weird logic that has to be applied to 
reverse sequencing, when I flip that around, I read the motor enable 
lines as directly swapped, and the drive select lines directly swapped. 
To punctuate: There is no exchange of Motor Enable with Drive Select.

If the BBC were to use any pinout other than that above, then using a 
straight cable with one BBC drive and one PC drive wouldn't work on a 
straight cable - the drive select lines would be incorrect, and one (or 
both) drives would be unselectable. Since this has been proven to 
clearly work without cable modification, we can logically conclude that 
the BBC isn't using bizarre drive select lines.

Regardless of what the BBC's interpretation of the connector is, the 
twist in the cable will not cause issues with enabling motors when it 
should be selecting drives and vice versa. It simply swaps the drive IDs 
around (both in terms of drive select and motor enable).

And where's this "its 1 and 2 not 0 and 1" come from? The connector 
supports a maximum of two drives. On my pinout they are marked A and B, 
but on almost every drive I have seen, the settings are for 0 and 1. 
Your statement implies that a third drive select line is present, which 
it is not.

The BBC Master may well support a DS2 line, but the floppy connector 
does not. Now if you want to personally refer to drive IDs using 1 and 2 
instead of 0 and 1, then thats your own business, but please refrain 
from criticising just because I use the more obvious numbering system 
(based on drive select jumper markings).

-- Richard