<http://www.classiccmp.org/mailman/listinfo/cctalk>
---snip---
There was a signal on some drives that came on the data cable.
I think it may have been a write protect but I don't recall
exactly what it was. The ST506 may have used this signal.
I'm not sure if this is what he is talking about.
There's a "drive selected" signal, but I think most drives have that.
It's there because the 34-way control cable is daisy-chained but the
20-way data cable is radial, one per drive.
Yes, that may have been it. If he is using just one drive,
this shouldn't be an issue.
I'd suspect things like step rate and number
of heads would
be more important to him than anything else.
The other important difference between the ST506 signals and the ST412
was that the ST506 didn't support buffered seek; the timing of the step
signals had to be slow enough that the stepper motor could keep up. The
ST412 was the first drive that buffered the step signals, so they could
be sent rapidly, and virtually every hard drive after that did too.
This is important because many drives that had the auto step, were
really slow using the fixed rate step. I had this problem getting
a ST251 to run on my Olivetti M20. The original drive had a fast step
rate of something like 6 ms. The ST251 wouldn't work faster than
10ms as I recall but the auto rate was much faster.
I think we need to hear from Andrew to see just what it is he
is talking about. From his original post, I still think he has something
confused.
Dwight
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-----REPLY-----
Hi,
Yes, I'll admit this can be a bit confusing and I am bit puzzled by it as
well. I had not heard of anything like it either but I have to believe the
VG engineer to know what he is talking about.
However, I have heard from a former Vector Graphic engineer who is
intimately familiar with the VEDMCS (aka, the integrated FD/HD controller)
and he tells me that the ST506's used for the VEDMCS are different than the
generic "off the shelf" ST506 hard drives. I believe the stock ST506 is
modified or configured to provide the signal in some manner.
The different signal is called a "constant index" signal. Apparently, it is
similar to an /INDEX signal from a floppy drive interface but the signal
tells the HD controller everytime sector 0 passes around. The HD controller
requires it for setting up the PLL.
Here is an excerpt on the subject from the VG engineer:
"
All hard drives working with a Vector FD/HD must have constant
index. There is a phase locked loop that is controlled by U20 which
is CMOS 4040 chip and unless you have constant index the PLL never
has time to sync up and gives read errors.
"
I have seen the VEDMCS driver source code and it specifically lists the
ST506 and the ST412 as its only two supported drives. I'd like to start
witho one of those and see if I can get it work.
Maybe I could convince it to accept a ST225 instead of a ST412 but so far I
haven't had any luck. I keep getting "drive not ready" errors.
I hope this helps explain this situation.
Thanks!
Andrew Lynch
