Looking for an 8 bit FDC...

[Allison]

>
>Subject: Re: Looking for an 8 bit FDC...
>   From: "Chuck Guzis" <cclist at sydex.com>
>   Date: Tue, 25 Oct 2005 11:22:55 -0700
>     To: cctalk at classiccmp.org
>
>On 10/25/2005 at 1:59 PM Allison wrote:
>
>>The 765A was least integrated but with the right external support more 
>>flexible than the 37C65 and later.
>
>You still have to put up with the "blindness' during the IAM interval and
>the lack of support for MFM 128-byte sectors--and the lack of support for
>non-standard address marks (not at all uncommon in old formats).  At least
>with the WD chips, you can read the raw track data.

Ah huh, what?  Who does 128byte MF sectors???  If you really have to it's 
possible to tell a 765 that it's a short sector in mfm. As to non standard 
address marks that was a tandyism and 765 "read deleted" works.

>>>The data seperator was a fairly simple circuit and could be done with
>>a counter or for improved results with a latch and prom.
>
>Or just find a nice little 8-pin WD 9216 data separator.   If you wanted
>more than that, a PLL might be the ticket.

If you can find one 9216 is good or the 9229.  IF not the latch/prom is
a synthetic PLL (which is the logic in the 9216 etal) and very good with
less headaches than a real PLL.

In general a 765A on a late XT or early AT class FDC is the trick
more possibilities than not.  Those that it can't be require extraordinary 
effort. 

There are few reasons that seem to abound for do alls. Those be "archives"
and I want to run a zzxxyy sim on a PC.  Those that most often archive
have a host that can read it.  The other case is obvious. However, the case 
I run into the most is I wish to run ABC on Northstar* under CP/M and need
to get it on to the AmproLB.  For that the Ampro connected to the serial port
of the NS* and MDM740 neatly sidesteps the "format problem" and once on the 
AmproLB I can run DOS and write it to a 720K 3.5" floppy under 
(DOS/WIN/NT/Linux) and run it under MyZ80 or whatever.


Allison