Date   : Thu, 23 May 1985 08:46:08 pdt
From   : "John A. Ellis" <jellis%marlin@nosc.ARPA>
Subject: Re: 8 inch drive problem

Your problem is not as weird as it may seem at first. The WD179X series
of disk controllers unload heads after 15 revolutions if no other command
has been received. The way it counts revolutions is by counting the index
pulses, which it couldn't do in this case. Also the problem with the drive
staying ready even after the index holes could not be detected is a problem
with the control logic on the Shugart SA800/801. We were using a power-down
circuit to shut off power to the drive motors and after much work found
out why our software would never detect that the drive was not ready. Shugart
fixed this problem on their 850/860 series. I'm not sure that all floppy
manufacturers had the same problem or not.
                                       John A. Ellis