Will The Grand Master Of Disk Controllers step foreward?

From: Richard Erlacher <edick_at_idcomm.com>
Date: Fri Apr 16 09:55:11 1999

-----Original Message-----
From: Eric Smith <eric_at_brouhaha.com>
To: Discussion re-collecting of classic computers
<classiccmp_at_u.washington.edu>
Date: Friday, April 16, 1999 1:45 AM
Subject: Re: Will The Grand Master Of Disk Controllers step foreward?


>> Specifically the WD-1000-5 disk controller. These are the ones that
>[...]
>> If you are intimately familiar with this legendary interface, I would
>> like to hear from you. I need to figure out how to modify it for 8"
>> harddrives.
>
>Regrettably I no longer have the manual or schematics for these, so a lot
>of this is from memory.
>
>The WD1000-5 was the WD1000 repackaged on an 8" * 5.75" board, to match the
>form factor of 5.25" drives.


There's more to the difference than that. For one thing, the WD1000 series
used the WD1100 chipset and an 8X300 microcontroller to run the whole thing,
while the WD1000-05 and -08, as well as the later models, used the WD1010
chip along with other combinations of the 40-pin support chipset of which
WD1014, which was, in at least one incarnation, an 8041.

>The original WD1000 and WD1001 had both 34 and 50 pin drive control
>connectors. I'm guessing that the WD1000-5 left the 50 pin connector out.
>However, you only need to scramble the pins appropriately, as the actual
>signals are the same. All odd pins are ground on both connectors; the
others
>should map thusly:
>
> 34-pin 50-pin signal
>
> 2 2 *RWC reduced write current
> 4 4 *HS2 head select 2
> 6 40 *WG write gate
> 8 8 *SC seek complete
> 10 42 *TK0 track 0
> 12 44 *WF write fault
> 14 14 *HS0 head select 0
> 16 NC
> 18 18 *HS1 head select 1
> 20 20 *IDX index
> 22 22 *RDY ready
> 24 36 *STEP
> 26 26 *DS1 drive select 1
> 28 28 *DS2 drive select 2
> 30 30 *DS3 drive select 3
> 32 32 *DS4 drive select 4
> 34 34 *DIR step direction (in when asserted)


This should look pretty much like 8" floppy disks. An early controller I
built used an FDC chip to drive these control signals, as the 8" Winchesters
had the same maximal step rate back then as the 8" double-headed FDD's.
That's overkill, and the FDC expects to see things from the data stream
which close the loop, and it won't see them. Open-loop, e.g. simple
head-positioning command operation is possible, at least to see if the
drive's mechanical functions are working. An enterprising approach would be
to operate the drive with a pair of small single-chippers one fairly slow
one to handle the head positioning, and the other a fairly quick one to
modulate the data, e.g. with ERLL code as was used in the PERSTOR
controllers.

>The radial data connectors are the same for both drive sizes.


Yes except that some drives extracted clock locally and sent it on the data
cable as well. For that reason, it would be advisable to stick with the
4.34 MHz data rate. Keep in mind, also, that while the wide cable is driven
with open collectors, the data cable is intended to be driven with
differential drivers/receivers of the MC3486/87 or 26LS31/32 type.

>The bigger problem is that 8-inch drives used a data rate of 4.34 Mbps
rather
>than 5 Mbps. I seem to recall that the WD1000 had a jumper setting for
this.
>If they removed the 50-pin drive control connector, they probably also
removed
>the jumper and supporting circuitry.


Western Digital was somewhat confused about how they should number their
controller models back in those days, and the scheme got muddled, but as I
recall, and I have some controllers to prove it, the data rate was fixed on
the board at the factory, in some cases, particularly the larger WD1000
boards with the WD1100 chips + 8X300 on board, had a discrete VCO as opposed
to the 74S124 or the LS624 they later used. These VCO's had to be tuned
quite carefully and a procedure was included in the instruction manual.
There were jumpers for accomplishing this tuning operation on nearly every
type of board in this entire family, but one needed both a crystal and a
retuned VCO for the PLL, not to mention changing the passive components in
the integrator (LPF) of the clock extraction circuitry. The process of
setting the VCO center frequency was not terribly difficult, but one had to
know which jumpers to remove at which stage of the operation because there
were inputs to the circuit which had to be active and other which had to be
passive at different stages of the operation.

>> Also, does anyone have docs for the Quantum Q-2040 8"
>> Winchester? I dunno what kind of power to feed it (24v sounds correct,
>> but I seem to recall it used 110vac also!), and so on.
>
>No data here, but almost certainly not 110 VAC. Probably 24V AC and 5V DC.


The power connections are precisely what is used with an 8" FDD, including a
110 VAC supply for the spindle motor. Don't forget that some 8" drives had
to be fed a negative 5V supply while others could swallow either -12 Vdc
or -5, depending on a jumper because they had on-board regulation. You have
to look for the regulator and ensure it has the jumper which bypassed it in
the correct position.

>You *might* be able to get a Q2040 to run at 5 Mbps, but I've never
personally seen it done.

We, meaning my people and I, tried this several times and never got it to
work reliably with Shugart drives. They did some signal processing on the
data, and included clock on the cable, so you might be able to skip the VCO
retuning if you can find the "right" place to inject this conditioned clock
in the data/clock recovery circuit. I'd be surprised to find the Quantum
drives did things much differently, as they had to be compatible with the
Shugarts, and some controllers, e.g. Intel's, relied on the drives or other
external circuitry to extract clock.
Received on Fri Apr 16 1999 - 09:55:11 BST