15 Sep
2009
15 Sep
'09
11:48 p.m.
On 14 Sep 2009 at 18:09, Steven Hirsch wrote:
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