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 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