Pinout for SED9421
cclist at sydex.com
Fri Nov 25 12:36:33 CST 2005
On 11/25/2005 at 9:59 AM Allison wrote:
>The all time worst was the 1771 internal data sep. Tandy initally did
>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).
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.
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