Pinout for SED9421

[Allison]

>Subject: Re: Pinout for SED9421
>   From: "Chuck Guzis" <cclist at sydex.com>
>   Date: Thu, 24 Nov 2005 14:19:32 -0800
>     To: cctalk at classiccmp.org
>Has anyone noticed a significant performance difference between the PLL
>type data separators (e.g. the WD1691/2143 combo) and the plain-Jane WD9216
>digital ones?  I suspect that the PLL type is more tolerant of drive speed
>variations, but that hardly matters all that much with modern drives.  I
>don't recall finding a disk that failed to read on a generic 9216-equipped
>FDC but read fine on the old IBM PC floppy board.
>
>Cheers,
>Chuck

I've used he 9216 and 9229 and the NEC apnote digital data seperator 
(prom state machine synthetic PLL) as well as a custom NEC ASIC (with
the prom data sep inside)  and they all do very well.  Testing against a
well developed PLL (not the WD animal) showed a small difference after a
4 days of continious read and writes (number of fails less than 3).  
You have to do a very large number of reads without external influences to
see the difference.  Power blips and the like were a pain.  A small 
difference was seen in the order of one of one failure per 250,000 reads
vs 1 in maybe 400-500,000 reads. You need a lot more testing than we did 
then to get near 1:10^8 stats with any validity.

FYI:the average PLL is a bear to build and debug, they required clean 
power and good board layout with ample groundplanes.  The digital ones are
very good, simple to layout and shift rates with only a mux.


Allison