Date   : Thu, 03 Apr 2008 14:40:39 -0500
From   : jules.richardson99@... (Jules Richardson)
Subject: Wires cut in floppy ribbon cable?

Kris Adcock wrote:
> So what does the cutting do? An idiosyncracy of the drive? I know that 
> alternate lines in a floppy cable are 0v, so presumably it's just the 
> one wire that is actually important.

Murky waters, indeed! :-)

Pin 1 is *nearly* always ground, but I've also seen mention of it being tied 
to +5V for drives which support some form of disk change reset option.

Pin 2 is similarly vague - most specs list it as an output for density select, 
  but I've also seen it documented as motor speed change, and also used as a 
(purpose unknown!) input rather than an output. Presumably some drives use it 
for other things, too (e.g. motorised eject, driving the access LED, head load 
solenoid etc.)

You're *probably* not missing anything by having it cut, but anything's 
possible...

> Not a big deal, I suppose - just something else to look out for when I'm 
> trying to build working drives from assorted non-working ones. :)

Grinding noises - hardware failure aside - might just be that you're trying to 
step the heads on the 'new' drive at a faster rate than it can handle. I 
*think* that the step rate is done via the keyboard links on the humble BBC, 
but I could be wrong there.

I can't remember off the top of my head how the BBC's expected cylinders, 
spindle speeds, head type and interface data rate compare to 5.25" drives in 
the PC world; I'm not sure that the two are particularly compatible (at least 
without changing drive jumpers) - plugging in something that's been pulled 
from a PC might not work. I *think* BBC drives are always 360rpm aren't they - 
whereas PC drives are 300RPM for DD and 360RPM for HD...

cheers

Jules