Pinout for SED9421

Chuck Guzis cclist at sydex.com
Mon Nov 28 13:47:44 CST 2005


On 11/28/2005 at 11:27 AM Dwight K. Elvey wrote:

> I don't know of any soft sectored that used serial
>chips. I suspect that it is because these depended
>on using illegal data clocking sequences in order
>to mark sectors. This would require more external
>circuits.

Some of the low end word processors (e.g. Smith Corona) used them (or a
feature of the MPU that simulated a serial chip).  No "illegal clocks",
just sync fields embedded in an idle stream.  SCM used 5F 5F 5F....16
followed by sector ID information and a CRC.  Works just fine.   Similarly,
Brother 240K diskettes do not use missing clocks, but rely on illegal GCR
patterns to denote start of sector ID.    I believe that the Future Data
systems used a similar scheme for their 8" media.  All are soft-sectored.

Cheers,
Chuck







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