Date   : Fri, 22 Feb 1991 09:02:21 PST
From   : sprague.wbst311@xerox.com
Subject: Motor on and Drive Select

Thanks for the responses.  I smoked my workstation monitor, so I'm a little
behind in my mail.

Zoltan Fekete Writes:

> From that time I have bad experiences with
> using Drive Select as Motor On. The main problem is that the drives
> usually report Drive Ready before they reach their nominal speed.

Ummm, some 5.25" drives don't even have a Drive Ready signal.  For example, the
SA400, SA450 and SA455.  Many of the 5.25" 1.2Mb drives give you a jumper to
select between Drive Ready and Disk Change.  Even so, my understanding of the
Drive Ready signal (and experimentation with it too) is that the signal works
differently than it does for a 8" drive.  I have the information on the 8"
drive, but do not exactly know how the 5.25" drives with this signal work.
I'll have to find out.

> So I would *NOT* suggest using simple AND logic to generate Motor on, or
> using Drive Select for that purpose. Rather I have two suggestions:
> 1. Tie Motor On to GND. Most of the drives are turning off their motors,

First, I still see no problem with the AND gate.  The real problem your
discussing is with the Drive Ready Signal.  To make things work, I had tied the
controllers Drive Ready signal to ground.  While it seems to work (and has
seemed to work for others), I would still agree that this is BAD.

Second, I did try to tie the Motor On Signal to ground.  I don't remember what
happened now, but I do remember that it did not seem a good solution.

> 2. Use more sophisticated logic (or combine with SW too). The Motor On should
>   work so, that when a drive is selected also Motor On becomes active, but
>   a logic delays the Ready signal to be active for a while (depending on
>   drive type, but usually 1-2 seconds).

Now your talking.  As having a working Drive Ready Signal makes the whole
system more reliable, this (hardware) is probably the path I will take.


Willy Writes:

> Most of the floppy varieties I have seen are jumperable to allow the
> MOTOR-ON signal to control the motor without also using DS.

The problem is that there is no Motor On signal on most 8" interface
connectors.  Since the motor is AC, and always on, there was no need for the
signal.  In any case, I have not been able to find such a jumper on the Epson
or Chinon 1.2Mb floppies that I have.  The Shugart drives (and I think the TEAC
drives) do have this jumper.

The problem is that this jumper may have disapeared on newer drives, since most
of these drives are going into PC's, and other computers that provide the Motor
On signal.  Someone mentioned that on some drives, the Drive Select 2 (or DS1
depending on whether it starts for 1 or 0) jumper was soldered in.  The Chinon
drive have the termination resistor soldered in, but there is a jumper labeled
TM, which I think disables the resister pack.


In any case, I am going to again try to jumper the Motor On to ground (on my
new Chinon drives).  I'll also start working on a delay circuit for the Drive
Ready signal.  I suspect that the delay can be quite a bit less than 1 to 2
seconds though.  Main problem will be in making sure I don't add noise to the
interface.


                               ~ Mike  (Sprague.Wbst311@Xerox.Com)