16 Sep
2009
16 Sep
'09
7:21 a.m.
----------------------------------------
From: cclist at sydex.com
To: cctalk at classiccmp.org
Date: Tue, 15 Sep 2009 23:48:05 -0700
Subject: Re: Intellec MDS questions
On 14 Sep 2009 at 18:09, Steven Hirsch wrote:
Hi
I don't think one can just take the same timing that was read
and write the bits back. Normally the controller adds some preemphasis
and deemphasis to make the timing right for the reads. For the
M2FM, this would require a little experimenting.
I do think the CW could do the job though.
What sample frequencies does it have?
Dwight
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I've read, re-read and re-re-read the
catweasel docs and still do not
have a clear picture of what the card really does and how one uses it.
If anyone can summarize it at a 10,000ft. level this would be greatly
appreciated!
It's *very* simple. The board has some SRAM (I don't know about the
IV, but earlier models have about 128KB) some counters and a little
bit of glue.
Note that a drive produces a pulse during reading when the polarity
of the magnetization of the media changes. So, when you write a
floppy, you feed the drive with a waveform that's either high or low
and on read, the drive produces a pulse when the writing waveform
switched states.
The CW can begin sampling at an index pulse or any arbitrary place--
similarly it can stop at an index pulse or any arbitrary place.
Basically, when operating while reading, the CW records the time
(from the last pulse) that a pulse arrives from the floppy drive.
This time is in the range of 1-127 clock times, with the clock
selectable from a short list of preset value and is stored, one value
after another in the SRAM.
When writing, the process is reversed.
Everything regarding interpretation of the pulse-time data produced
by the CW is done in software. Same goes for writing. Compared to
the CW, a PC floppy controller has monumental intelligence.
Before the CW IV, even signals to step the head from cylinder to
cylinder were generated by software.
--Chuck