Pinout for SED9421

[Allison]

>
>Subject: Re: Pinout for SED9421
>   From: "Chuck Guzis" <cclist at sydex.com>
>   Date: Fri, 25 Nov 2005 10:36:33 -0800
>     To: cctalk at classiccmp.org
>
>On 11/25/2005 at 9:59 AM Allison wrote:
>
>>The all time worst was the 1771 internal data sep.  Tandy initally did
>that to save parts. Really bad.
>
>I remember once asking our FDC design guy (he cut his teeth at Sperry ISS)
>about the 1771 on-chip DS.  He just laughed and gave a thumbs-down.  He
>built his board around the 1781, using GCR and a bit rate of about 380 KHz
>on DS media.  The drive electronics needed the low-pass filter tweaked a
>bit to work, but he managed to get about a megabyte on a 5.25" DS floppy.
>Not too shabby for the time (1979).  

Tandys EI design got me a few trips to FtWorth to massage their heads 
with a bat for what they did.

Yes, 1meg was way above the usual 190k-380k common for for DDDS drives.
The highest I got to with MFM was 800k (80tr 2sided).

>Drives back then tended to have more problems than the controllers did.  
>
>In particular, we gave up on Micropolis because of their stubborn
>insistence on using a leadscrew positioner, long after almost everyone else
>went to the faster taut-band.  I still have a 96 tpi Micropolis drive that
>employs buffered seek (goes not ready while seeking).  It also mounts the
>drive electronics board and the positioner on the movable part of the disk
>clamping assembly.  Only the drive motor and tach circuit is mounted on the
>stationary drive frame.

The disk that Shugart used while innovative was really bad for repeatability 
of position and slooowwww. 

Allison