1 Jan
2008
1 Jan
'08
6:24 a.m.
Date: Mon, 31 Dec 2007 18:07:38 -0500
From: "Andrew Lynch" <lynchaj at yahoo.com
<http://www.classiccmp.org/mailman/listinfo/cctalk> >
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:
Well, the ST506 knows nothing from sectors--it's about as "bare" and
interface as they come. I wonder if by "constant index" it's meant
that there's always an INDEX/ signal present; not just when the drive
is selected. At least that would make sense from this:
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...
Maybe? What happens if the drive is jumpereed so as to be
permanently selected?
Cheers,
Chuck
-----REPLY-----
Hi Chuck,
Yes you are correct. I spoke with the VG engineer to get more details on
"constant index" and you described it exactly.
Apparently there is a cut and jumper modification which can be made to the
ST506 circuit board to bring the /INDEX signal to the interface constantly
even when the drive is not selected.
Once I get a ST506 drive I will find and make the modification. Assuming I
can get the ST506 to work, I will try making modifications to ST225's or
other more common hard drives.
I'd like to get the standard case working to establish if my VEDMCS is
working properly before adding in other variables of different drives etc.
Thanks!
Andrew Lynch
1 Jan
1 Jan
8:55 a.m.
From: lynchaj at yahoo.com
---snip---
Hi Chuck,
Yes you are correct. I spoke with the VG engineer to get more details on
"constant index" and you described it exactly.
Apparently there is a cut and jumper modification which can be made to the
ST506 circuit board to bring the /INDEX signal to the interface constantly
even when the drive is not selected.
Once I get a ST506 drive I will find and make the modification. Assuming I
can get the ST506 to work, I will try making modifications to ST225's or
other more common hard drives.
I'd like to get the standard case working to establish if my VEDMCS is
working properly before adding in other variables of different drives etc.
Hi Andrew
When you find your drive, it should be easy to make the mod.
Follow the signal back from the pin. There should be a line
driver there. Usually something like a 74S38 or a 7545x.
These usually have two inputs. Using a scope or a logic probe,
you'll see one input with the index and the other will be
static. The static one is the one to tie high to get a constant
Index. The easiest way is to cut the IC lead near the board
and lift it away a little. You can then put a pullup resistor
on this lead.
I like doing this more than cutting the circuit board.
If restoring, one can replace the IC or just bend the lead back
solder it back.
Dwight
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9:14 a.m.
Hi Andrew
I forgot to mention. The ST506 doesn't have an auto park.
This means that shipping can be a problem. The drive needs to
be parked before it canbe safely shipped.
Failure to park it can damage the early tracks that you'll need
to get it working on your system.
Dwight
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11:48 a.m.
Apparently there is a cut and jumper modification
which can be made to the
ST506 circuit board to bring the /INDEX signal to the interface constantly
even when the drive is not selected.
Once I get a ST506 drive I will find and make the modification. Assuming I
can get the ST506 to work, I will try making modifications to ST225's or
other more common hard drives.
It would eb useful to find out the modifaction (to either an ST506 or
ST412) anyway. One of us with the approriate schematics (I am pretty sure
I have both...) can then work out what's going on, what signal is tapped
off 9and where), and what pin it's brought out to.
My _guess_, and it is just a guess, is that the index siganl is tapped
off immediately before the output driver (which normally only feeds the
index signal onto the control cable (34 pin) when the drive is enabled),
and this siganal is wired to one of the many unused pins on the data (20
pin) connector. That way the controller can always seel the index signal
of all the drives in the machine
-tony
6201
days inactive
6201
days old
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