2 Jun
2011
2 Jun
'11
11:01 a.m.
Johnny Billquist wrote:
Correct the cable from the RQDX1/2/3 is 50wice and looks like the same
used for
old school SCSI but it's not. It's all the address and control lines
All that was in the 5V lines were severl in parallel and the early cable
the wires were unequal length and made for current hogging at heavy bus
loads. The fixed cable had all
the leads of equal length to avoid this. If the older cable is used for
light bus load there are no issues but watch for heating ( or
overheating) of the pins on the shorter wires.
On 2011-06-02 07.56, <arcarlini at iee.org>
wrote:
Correct to a point. The base panel is wired a lot like the twisted
floppy cable of PCs.
It was intended to have a hard disk and a floppy and the device
addresses are plug assigned.
If you put in two hard disks with standard jumpers they both try to talk
at the same time
as the same device... bad!
However, if the drive address is jumperd correctly it works fine however
the correct jumpers are not given. I derived it by tracing wires.
Johnny Billquist [bqt at softjar.se] wrote:
It's not an issue with two drives, per se, but an issue with the built
in distribution panel.
> As far as I know, the BA23 backplane
distribution panel can*not* be
> used for two disk drives. I know there is a DEC note/article
> about this
> not working. You need the external distribution board for the
> RQDX3 to
I used several configs in the DEC lab with 2 RD54s in a BA23 for
years
and never hit a problem. (Mind you, I also had a KDA50 in a BA23, so
I'm not saying you should do this at home :-)). If there's
a note, I'd like to see it sometime ...
I'll try to locate it. I know I have it somewhere in paper form, but
hopefully it's been scanned somewhere on bitsavers, since all my
papers are far from me.
On 2011-06-02 07.56, "Rod Smallwood"<rodsmallwood at btconnect.com>
wrote:
Two hard drives in a BA23?
Like I said above. It's not the question of two drives in the BA23 as
such. It is the built-in distribution panel that is the problem.
Provided you don?t want to connect to another
BA23 or use a non-DEC disk
controller then a brace of DEC SCSI drives and a flat SCSI cable will
do it.
SCSI disks have even less to do with it. :-)
from the RQDXn
for all possible devices (up to 4
MFM disks or 3 and 1 RX50). The back
plane distribution board of the BA23 (and a different one in the BA123)
breaks this out to the cable pairs used for MFM or the single 34 wide
for RX50 or RX33.
I think the
drive power cables come direct from the PSU. If so, then
you can
rip out the backplane and card guides. The guides can be used to make
storage units for PC cards. You can use the back plane to make a real
'open'
system i.e. one you can get at the pc cards.
Yeah, the power cables comes from the PSU, and yes, there was an issue
with those on some BA23. But that is something else. And just using
the box as a shelf is obviously also not a problem.
On Thu, 02 Jun 2011 08:20:11 +0100 Pete Turnbull
<pete at dunnington.plus.com> wrote:
drive
There is enough reserve on the 12V line that it works well. Keep in
mind DEC
only qualified certain configurations. If you not using all the 12V on
the bus then
you have excess for the RDs. I've found that this was not an issue and
heat
On 01/06/2011 18:23, Johnny Billquist wrote:
>> >> I remember_trying_ to put two hard disks in one machine for
quick
>> >> disk-to-disk copies. I have a
fuzzy memory that it didn't
work for
>> >> me, but I don't remember
whacking either drive to the point
that they
>> >> didn't work when returned
to their former homes.
> >
> > As far as I know, the BA23 backplane distribution panel can
*not* be
> > used for two disk drives. I know there
is a DEC note/article
about this
> > not working. You need the external
distribution board for the
RQDX3 to
> > use two drives. If you use the BA23
backplane distribution panel
with
> > two harddisk drives, you have a high
chance of corrupting both
disks.
> > (If I remember right, the write gate
signal somehow goes to both
disks,
> > no matter what, which cause the disk to
possibly start writing
when the
> disk
is seeking, for example. Very bad.)
Although some manuals do mention that you
should only use one hard in a BA23 (eg the Maintenance Manual) I've
seen several systems --
including mine -- do so with no problem. I've never seen a problem
with
Write Gate, nor would I expect to. Like all
other ST412-type
interfaces, the M9058 distribution card has the same write gate signal
wired to all the 34-pin HDD connectors in parallel. In fact the /only/
control signals not wired strictly in parallel on those connectors are
some of the drive selects.
The M9058 is the RQDXE. Don't anyone ever read what I write, or am I
really that bad at expressing myself? I wrote "the BA23 backplane
distribution panel". That is *not* the RQDXE.
With the RQDXE it works just fine.
What I do know is that the docs say you must draw
no more than 7A from
the 12V supply in a BA23, and one RD51 takes 4.5A. So 2 x RD51 would
overload it. I believe that's the only restriction, because putting a
second RD5x in a BA23C expansion box, connected via an RQDXE, was
supported -- and AFAIR the RQDXE doesn't do anything clever with the
control
or status signals.
from the drives more of a concern (two RD54s!)
Keep in mind an allowed configuation was RD54 and TK50 for MVII systems.
Yes, the power supply is a separate issue. And yes,
there is no issue
putting two drives in the same BA23 if you use a RQDXE. However, if
you plug in two drives using the built-in backplane distribution
panel, you will have a disk crash, which I unfortunately have first
hand experience of having to clean up after. The formatting of one, or
both drives, will be destroyed, and you will need to reformat the
drive to be able to use it again, if reformatting is possible. I never
tried that, as I wanted to get as much data as possible off the two
drives, and afterwards, the machine got SCSI drives instead of the RD
drives, as you might as well upgrade when you were working on it.
Initially when
trying to put two drives in I had that problem. OOps!
Fortunately I had a VS2000 to reformat rather than boot XXDP on the
11/23+ reformat the drives. Its non-distructive in that MFM drives can
be low level formatted with out issue and
some like the RD32 seemed to need it frequently! The reason for needing
to reformat
is that when you turn on write is important and is timed off the data
and for two drives in parallel (same device address) they will never be
in data sync (other than by accident).
Once I figured out the address needed for the second drive and then
reformatted it
was fine that way.
Allison
Johnny