Pinout for SED9421

Dwight K. Elvey dwight.elvey at
Mon Nov 28 13:58:02 CST 2005

>From: "Chuck Guzis" <cclist at>
>On 11/28/2005 at 10:46 AM Dwight K. Elvey wrote:
>> Besides the HeathKit hard sectored controller board,
>>used on both the H8 and the H89, Polymorphics also
>>used a serial chip to do data. In both of these
>>cases, as you state, they used synchronous serial
>>chips and not async.
>To put a reverse twist on this, has anyone ever used two floppy controllers
>to transfer data between two systems?  I know it'd take a little extra
>hardware (something has to provide address headers outside of a format
>operation), but it should still be quite possible to do so.
>I've never tried, however.  Ethernet is so much easier.

 I've used slightly modified cassette tape software
to transfer data to and from a Poly88 to a PC. The only
part I recall changing was the initialization code and
the sync detect. They used a 8251 so there was little
other modifications. The Poly88 thought it was otherwise
just doing a tape transfer. I initialized the 8251
as async to match the PC end.
 I suspect that one could do a controller to controller
method but one would need to generate the index pulses.
A simple 555 circuit would most likely be enough.
 You might need to add a little analog filtering to
match up the compensation that is usually added to the
write data on the higher density drives.

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