Date   : Fri, 14 Oct 2005 16:16:46 +0100
From   : Jules Richardson <julesrichardsonuk@...>
Subject: Re: 3.5" Floppy For A Master

Eelco Huininga wrote:
  >> A 3.5" drive detects the disk type by noticing the second hold on
>> a HD disk. That's one of the reasons you shouldn't fake a HD disk
>> to DD by covering the hole, 'cos the drive will then use the wrong
>> write current to write to the disk and ruin it.
> 
> Hmmm I always thought HD drives could be switched between the DD and HD 
> modes by an extra input signal (pin 2 I think). So if drives auto-detect 
> the density of floppydisks, what is this signal for then?

pin 2 gets used for all sorts depending on the drive - density select, 
speed control, motorised eject control, LED control etc.

Far as I know, there's no particular standard that governs what it gets 
used for, nor whether it's an input or an output (which is why it's 
worth checking what drives you have before blindly hooking them up to 
any machine!)

Going from memory, there are a couple of other pins which aren't 
*always* the same on drives, although 99% of them share the same 
functionality - pin 2 is much more open to interpretation.

cheers

Jules