Reanimating a PDP-11/23
ethan.dicks at gmail.com
Tue Dec 1 09:01:23 CST 2009
On 12/1/09, Pontus Pihlgren <pontus at update.uu.se> wrote:
> I'm somewhat confused by this, I know how and why you need grant cards
> in a Unibus machine. But I thought the Qbus made away with that need,
> although I have read something about it being needed for certain cards
> and that some controllers need to be the last card.
The "difference" in terms of grants and slots and jumpers is that you
don't have to modify your Qbus backplane to have a DMA-capable (NPR -
non-processor request) card in a single slot, but you do for Unibus.
The Qbus still has a grant chain for interrupts just like the Unibus.
There is a Qbus grant card, M9047, that looks very similar to the
Unibus G727 (and descendants) grant card, but the bridged pins are
slightly different (and the handle is Magenta, not Green). When we
were making Qbus and Unibus periperals, we stuffed one of our own
Unibus grant cards (w/NPR jumper) in every box - I wanted to make a
version that could be rejumpered to work in a Qbus backplane, but we
had so many Unibus grant cards on the shelf that we never needed to
order more cards.
> Anyway, I have mine in the order: CPU, MEM, SLU, TERM, with
> some space between for easier handling.
The order is fine, but unless you have no blank slots between the CPU
and SLU, you might have problems. Thanks to Pete for reminding me
that you can have space above the BDV-11 and it won't matter. It's
been a few years since I loaded up a Qbus (all of mine are pretty well
set these days).
The card that really matters is the RQDX1 - you can't put things
behind it because it doesn't pass grant. DEC broke their own rules
there, but since they expected you to install the RQDX1 in a BA23 and
the cable for the distribution board comes up from the bottom, there's
little reason *not* to put the RQDX1 in last. It doesn't have to be
in the bottom-most slot of the entire backplane, but it does need to
be the bottom-most installed card in the backplane.
> The backplane is not the serpentine version, when I got it, it had a
> RL01 controller in it (I got two RL01 drives too) which I believe need
> the straight backplane.
That should be the "CD" backplane (can't remember the part number). I
have one like that, with an RLV11 as well. Yes... dual-height cards
just stack down the left edge.
> I will check the console cable, it came with the machine but is home
> made, it goes directly from the card (i.e. no cab kit). I'm fairly
> certain of the baud speed, the manual was quite clear on the jumpering
> on the DLVJ1 (I call it that because the pdp-11 field guide lists it as
If you are going right into the SLU card, check that you are in the
correct port (all the way left or all the way right - I'd have to go
look at a machine or read the handbook to be certain), and do check
the baud rates. Of course what we usually did when we weren't sure of
the baud rate was to set the terminal to the most common ones and poke
at it - it was faster to check 3-4 baud rates that way (300, 1200,
9600, at least) than to tear apart the machine. If that didn't work,
we did it the long way and examined the hardware. Of course, as
pointed out further up this thread, there are some details about the
specific wiring for even a direct cable - the necessary information is
in the Microcomputer Peripherals Handbook - some DEC serial
connections are straight RS-232 (1488/1489 drivers), some are
differential (9636/9637drivers) and may require a jumper or converter.
As for the name, when it first came out in the 1970s, it was called
the DLV11J, since other SLUs were the DLV11E, etc. DEC started
renaming certain cards with the newer Qbus convention (RQDX1, et al.)
in part, I think, to get rid of the '11' and in part to reassure the
customers that this card will work in a VAX - thus DLVJ1. The
renaming might have worked for other cards, but I have honestly never
seen a DLV11J (or DLVJ1) in a MicroVAX, only in a PDP-11, so for me,
the old name will stick.
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