Date   : Sat, 18 Nov 2006 11:18:57 +1000
From   : bdevries@... (Bob Devries)
Subject: Unusual piece of equipment available.

Richard, you said:
> I can't be certain on this (given recent discussions on step rate, etc),
> but the cable is routed via a small circuit board with a couple of ICs
> on it before it gets to the drive.
>

I have seen this on a Tandy Colour Computer. The circuit was described in 
"The Rainbow" at one stage, and it does indeed issue a second step pulse 
upon receipt of the first. It actually shortened the original step pulse 
considerably, which could cause problems when very short stepping pulses 
were already used.
I'll see if I can dig up the schematic.

--
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: "Richard Gellman" <splodge@...                   >
To: <bbc-micro@...               >
Sent: Saturday, November 18, 2006 11:15 AM
Subject: Re: [BBC-Micro] Unusual piece of equipment available.


> Jonathan Graham Harston wrote:
>>> Message-ID: <45492360.7020500@...                   >
>>>
>>
>> Richard Gellman <splodge@...                   > wrote:
>>
>>> What we have on offer here is a floppy disc drive cable (of the BBC
>>> Micro variety) with one edge connector on the end, but fitted with a
>>> switch to convert an 80-track drive into a 40/80 switchable.
>>>
>>
>> How? There are no connections on the disk drive connector to
>> control the number of tracks or the stepping rate. Some disk
>> drives have links or pads on them that a switch can be wired to,
>> but that is on the PCB, not on the drive connector.
>>
> I can't be certain on this (given recent discussions on step rate, etc),
> but the cable is routed via a small circuit board with a couple of ICs
> on it before it gets to the drive.
>
> My guess is its issuing a second step signal on receipt of the first,
> thus making an 80 track drive double step, effectively becoming a 40
> track drive. I imagine the switch simply bypasses this add-on board for
> 80-track mode.
>
> The switch itself was somewhat crudely fitted to the rear of the metal
> case, the drive itself have no track switching on it whatsoever. The
> "upgrade" also require two wires soldering the power connector for it to
> work.
>
> I've had one email of enquiry on this, but they've since not got back to
> me. If I don't hear from them in the next couple of days, the cable is
> yours.
>>
>>
>>> The cable is available to any interested party, free of charge, and I
>>> won't even ask for postage costs :)
>>>
>>
>> I'll add it to my collection of "odd stuff", aka take a photo and
>> put it in the basement :)
>>
> I can provide a photo (JPEG) of it if you want a better idea of how it
> does what it apparently does.
>
> -- Richard
>>
>>
>
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