Pinout for SED9421

[Allison]

>
>Subject: Re: Pinout for SED9421
>   From: "Chuck Guzis" <cclist at sydex.com>
>   Date: Fri, 25 Nov 2005 09:24:30 -0800
>     To: cctalk at classiccmp.org
>
>On 11/25/2005 at 9:31 AM shoppa_classiccmp at trailing-edge.com wrote:
>
>>to do the tweaking, as well as field service, as well as ...
>>(Of course us hackers don't mind!)
>
>I've got a system here with a rather elaborate analog data separator PLL
>(built around a CA3130 op amp).  Part of the manufacturing process involves
>a calibration diskette, trimpot and scope.  It's pretty robust once it's
>been set up, but component aging is probably a significant factor in
>long-term performance.
>
>It seems hardly any more robust than a plain old digital (9216-type) data
>separator.  Which makes me wonder why anyone would bother implementing the
>data separator in Figure 13 of the 179x app notes (3 trimpots).

Simple, the non-digital circuits were available and the chips like 9229/9216
were later. There were really three varients, for plain FM oneshots either
analog or digital did the job well enough.  When DD (MFM) started to appear
along with then current drives That didn't work well enough (peak shift) 
and PLLs became the solution then around 1981 people started to figure out 
how to apply write precomp and digital data seps that were either counter
based or DPLL.

>Out of the stats on performance that Allison cited, how many of those
>errors could be recovered with a simple retry?

Most were soft.  Once they started to become hard the media was showing 
distress.

>When I learned that Jameco was running low on 9216's, I bought their entire
>stock, which amounts to about a 2 ft. tube of 8 pin DIPS.  So if you're
>looking for one, you know who's got 'em.  :)

Either that a Dflop(74LS74), hex D-latch(74LS174) and 32x4 prom(74LS288).


Allison