Date   : Fri, 10 Jul 2009 21:42:02 +0100
From   : acorn@... (Andy Ford)
Subject: Master Compact Drive Cable

Thanks Pete.

I don't have easy access to the machine for a day or so now, but your 
information has given me a few idea's and thoughts. :)

I should add, the drives are original Sony drives (identical) as when I 
was given this machine both were set (via the switch on the side) to DS0.

I'd guess I have to chop the termination out of one of the drives then 
at least.


Andy. :)



Pete Turnbull wrote:
> 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!
>
>