Looking for an 8 bit FDC... - test-drb@ccmp.vtda.org

25 Oct 2005

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Subject: Re: Looking for an 8 bit FDC...
   From: "Chuck Guzis" <cclist at sydex.com>
   Date: Tue, 25 Oct 2005 10:46:34 -0700
     To: cctalk at classiccmp.org

On 10/25/2005 at 5:28 PM Jules Richardson wrote:

 Intel's 8271 looks like a possibility at the
moment, but I thought I'd 
poll the list for alternative ideas too. FM support is of course 
critical - MFM is less of an issue as the host PC can handle that. 
The 8271 is a pile of worms.  Don't even bother with it. 
The 8271 was SD only as well.

...
 In a DIP package, if you want to restrict yourself to
5.25/3.5" MFM and FM
(but not HD) formats, the WD 1770/1772 is a nice compact (28 pin)  little
chip that includes motor control lines as well a decent data separator for
FM and MFM.  The Atari ST used it.  If you want something a bit more
elaborate, the WD 279x series will handle most of what you need to handle,
but in a 40 pin package.  All are easy to program and have Z-80 friendly
signals. 
The 279X is a more integrated 1793 so thats a good choice too.

Watch out for the 1770/72 as not all flavors of them will work at 8" data
rates.

...
 The NEC 765-based chips (National 8473/8477, WD 37C65, 
Intel 82077, etc.
(the list is very long)) are built for the PC market and, when viewed from
the aspect of reading the largest number of formats, are quite quirky.
Some will read FM, but not write FM; some will drop the first sector if the
IAM missing (many WD-based vintage computers didn't bother with it), few
support 128-byte MFM sectors, etc. etc.   Some of the older chips require
that you supply your own data separator.  Given the choice, I'd stay away
from them.  
The 765A was least integrated but with the right external support more 
flexible than the 37C65 and later.

The data seperator was a fairly simple circuit and could be done with
a counter or for improved results with a latch and prom.

Allison