12 Aug
2023
12 Aug
'23
11:45 p.m.
From memory, when I looked into doing this I found that the RQDX3 BA23 distribution panel
maps DS2 from the contriller to all DS pins on the B cable of one drive and DS3 to all DS
lines on the other. I never did test the theory though. I did not get a special adapter
from decromancer.
Hope it helps
Nigel
On August 12, 2023 6:35:35 p.m. EDT, Peter Coghlan via cctalk
<cctalk(a)classiccmp.org> wrote:
I have a Gesswein MFM emulator from decromancer.ca; who offer an adaptor
that yields a 2nd MFM data connector.
I'll use mine in a Microvax 2000. Does anyone know how to hook it up as
two MFM drives in a Microvax 2000?
The vendor sold a 1in high adaptor box, BA40A, with DD50 connectors to a
second cabinet (same as CPU box) for a second drive.
DEC configured both primary and secondary drives identically (drive 3, IIRC).
The Microvax 2000 Technical Manual gives the pinout from the mother board
to the MFM/floppy daughterboard, but I can't find the pinout from that
daughterboard to the cables anywhere.
I've been looking for a BA40A, for some years now, to trace the pin layout
for a 2nd drive. Does anyone know it?
Has anyone successfully configured a single MFM emulator as two MFM drives
in a Microvax 2000? Or to an RQDX3?
I've had two real MFM drives running with one of my VAXstation/MicroVAX 2000
machines but it is a long time since I've looked at this stuff so I'm not
certain of the details.
I didn't use any adapter box or cables with DD connectors. I only had the
original DEC ribbon cable that connects from the VAX motherboard to one MFM
drive and one RX33 floppy drive. I used this as a guide to make up a new
longer cable with an extra 34 pin edge connector in parallel with the first
MFM drive control connector. I ran this cable out through the hole in the
bottom of the case where the cable to the adapter box was intended to run
so that the added connector could be placed on an external MFM drive.
I also connected a straight through 20 pin IDC to edge connector ribbon cable
salvaged from a PC from the vacant 20 pin IDC connector on the VAX motherboard
to the data connector on the second MFM drive, running it out through the
same hole in the VAX case.
IIRC I had to jumper the second MFM drive as drive 4. Presumably I should
have made a twist in the cable to allow the second MFM drive to be configured
as drive 3, the same as the first drive.
I think the first MFM drive showed up as DUA0, the second one as DUA1 and the
floppy as DUA2.
I recall an incident when I tried to connect one particular second MFM drive
externally and the VAX refused to power up. It seemed the overcurrent trip
was operating in the power supply and the extra drive appeared to be the
cause of this. I'm a bit hazy on exactly what I did to try to get around
this issue, I suspect I tried powering up the VAX with the drive disconnected
and connecting it after power up. Anyway, the upshot was that one or two of
the conductors in the 20 pin data cable got extremely hot and the insulation
on them started to smoke before I quickly switched off. I'm not sure but I
think the reason was that the particular drive placed an unfused +5V on some
pins on the data connector and the corresponding pins were grounded at the
VAX end. Or it could be the other way around... Luckily there was no damage
to anything other than the cable.
Regards,
Peter Coghlan.