25 Oct
2005
25 Oct
'05
3:42 p.m.
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:
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 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. The data seperator was a fairly simple circuit and
could be done with
a counter or for improved results with a latch and prom. 
25 Oct
25 Oct
4:46 p.m.
>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.
On Tue, 25 Oct 2005, Allison wrote:
Ah huh, what?
The IAM interval is easily handled by masking that signal. (interrupt the
cable, or (on older cruder drives) cover the index with tape.)
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.
I have half a dozen formats that I was unable to put into XenoCopy,
due to 128 MFM. I never could get reliable reading, so I did those with
a 1791.
As to non standard
address marks that was a tandyism and 765 "read deleted" works.
I don't remember any non-standard address marks other than Tandy, but
there could have been.
'course the 1791 didn't want to write all of the ones that the 1771 did!
I understand that the 765 multi-sector "track read" was better for MOST of
the market, but WE would rather have had the WD style "raw" track read.
--
Grumpy Ol' Fred cisin at xenosoft.com
5:44 p.m.
On 10/25/2005 at 1:46 PM Fred Cisin wrote:
The IAM interval is easily handled by masking that
signal. (interrupt the
cable, or (on older cruder drives) cover the index with tape.)
I did better than that--I inserted a flip-flop and a gate to optionally
pass the index signal every OTHER rev. But why do it if you don't have
to?
I have half a dozen formats that I was unable to put
into XenoCopy,
due to 128 MFM. I never could get reliable reading, so I did those with
a 1791.
I believe that Don Maslin discovered that any adapter with a National 8473
would do the trick (but not the 8477, strangely enough).
Whatever, stay away from the Intel 82077AA-1 chips--they cannot write FM.
When I asked an Intel application engineer about why Intel broke this
capability (the 82077 could do the write), his answer was "who writes FM
diskettes anymore?". You see this kind of thinking in the current crop of
USB floppies.
I don't remember any non-standard address marks
other than Tandy, but
there could have been.
'course the 1791 didn't want to write all of the ones that the 1771 did!
I'd have to dig through my notes, but there were a few others. I've got a
couple WD 1781's here; I take it that they're a pretty rare bird...
I understand that the 765 multi-sector "track
read" was better for MOST of
the market, but WE would rather have had the WD style "raw" track read.
No kidding.
Has anyone ever used the Signetics 8x330 bit-slice floppy controller? Like
most of the 8x300 line, a very strange bird.
Cheers,
Chuck
26 Oct
26 Oct
5:39 a.m.
(All always, the list management is broken, I don't have Allison's posting
yet, but the answers this posting...)
On Tue, 25 Oct 2005, Fred Cisin wrote:
The IAM interval is easily handled by masking that
signal. (interrupt the
cable, or (on older cruder drives) cover the index with tape.)
As a note: The IAM is not defined by the IBM standard, there's no IAM on
3740 (FM) or System/34 (MFM) diskettes.
On Tue, 25 Oct 2005, Allison wrote:
> 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.
Robotron for examples uses 128 bytes/sect. MFM so they have 26 sectors per
track on a 96 tpi DD 5.25" diskette and have the standard 8" FM sector and
track layout.
I have half a dozen formats that I was unable to put
into XenoCopy,
due to 128 MFM. I never could get reliable reading, so I did those with
a 1791.
I have several PCs and Multi I/O ISA controller cards that can do 128
bytes/sect. MFM. Watch out for the NatSemi DP8473 FDC.
Christian
6849
days inactive
6850
days old
3 comments
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