ST506 and/or ST412 hard disk drives - test-drb@ccmp.vtda.org

31 Dec 2007

...
   From: pete at
dunnington.plus.com  ---snip---

 There was a signal on some drives that came on the data cable.
 I think it may have been a write protect but I don't recall
 exactly what it was. The ST506 may have used this signal.
 I'm not sure if this is what he is talking about. 
 There's a "drive selected" signal, but I think most drives have that.
 It's there because the 34-way control cable is daisy-chained but the
 20-way data cable is radial, one per drive. 
  Yes, that may have been it. If he is using just one drive,
 this shouldn't be an issue. 
Actually it would be if the controller depends on it, even if you only 
have one drive. If that drive doesn't output the 'drive_selected_ signal, 
then the contorller might not enable any data receivers.

...

  I'd suspect things like step rate and number
of heads would
 be more important to him than anything else. 
 The other important difference between the ST506 signals and the ST412
 was that the ST506 didn't support buffered seek; the timing of the step
 signals had to be slow enough that the stepper motor could keep up. The
 ST412 was the first drive that buffered the step signals, so they could
 be sent rapidly, and virtually every hard drive after that did too.

   This is important because many drives that had the auto step, were
 really slow using the fixed rate step. I had this problem getting  
The really strange lone (not the same interface, of course, but similar 
in concept) is the SA4000 (14" Winchester). On that drive, you eitehr 
have to send pulses so slowly that the the head movement it completed  
for each one (that is, the head gets to the next track before you send 
the next pulse) or  fast enough that you've sent all of them before the 
heads start to move. An intermediate rate will end up with the darn thing 
mis-stepping. This is docuemtned in the manaul and the reason for it 
(one up/down counter with a common clock input to record the head offset) 
is clear from the schematics.

-tony