Date   : Fri, 10 Jul 2009 18:27:23 +0100
From   : pete@... (Pete Turnbull)
Subject: Master Compact Drive Cable

On 10/07/2009 11:33, Andy Ford wrote:

> I am about 90% of the way there now with this. I looked at the diagram 
> for connecting a 5.25 drive , which although not quite right gave me a 
> good clue (pin 1 on the Compact goes to pin 8 on the standard floppy 
> connector, so it's not fitted at one end as such)

That sounds right; pin 1 on the Compact is /INDEX, and /INDEX is pin 8 
on a standard 34-pin floppy connector.  You should also end up with 
nothing connected to pin 34 at the floppy end, as you run out of wires 
in the ribbon cable at pin 32.

> I have since made a good cable up (cutting down a length of floppy 
> ribbon cable) , however I have the following problem (bear in mind I 
> have two drives connected, but with just one it is still the same) , 
> interestedly the drive light does not work.

That may depend on the drive setup.  There's no signal on a floppy 
interface that corresponds exactly to "turn on the LED".  Many drives do 
this in different ways, some for example just turn on the LED in 
response to the Drive Select line, but some need this and also either 
Motor_On (pin 16) or In_Use (pin 6).

> I "think" I have it either a pin out (ie: fitted too far across) or I am 
> missing something (as from all the photographs I have seen, there is a 
> small link between a couple of pins on the data cable)

Apart from the shortage of pins, and one jumper, the Compact floppy 
interface is pretty standard (SA400 standard, not the bastardised IBM PC 
kludge with a twisted cable).  So the drives ought to be set to DS0 and 
DS1 respectively -- and that matches the information in the Service 
Manual.  Make sure that one drive (and only one) has terminators fitted. 
  Improper termination is a common cause of bad data reads.  Also make 
sure that C10 (which is a small capacitor near the 1772) is fitted. 
Another possibility is that a modern drive may not have enough oomph to 
drive a properly terminated signal line.  The Compact has the correct 
value (150 ohm) terminators installed but some modern 3.5" drives can't 
handle lower resistance than about 1K ohm.

One odd thing about the Compact interface is the presence of a jumper 
called PL3 (normally not fitted) between the DS2 Drive Select line 
(which isn't normally used, only DS0 and DS1 are) and ground.  I can't 
remember what that's for!

-- 
Pete                                           Peter Turnbull
                                               Network Manager
                                               University of York