2 Feb
2010
2 Feb
'10
1:36 p.m.
As I slowly dig into "my" new 11/34A, I'm amazed by the bus configuration.
Starting from the CPU, the main BA11 chassis has a double (9-slot) system unit, joined to
a single (4-slot) SU by an?M9202 jumper. From the last slot in the chassis, a Unibus cable
runs to a junction block on the cabinet back door. A second cable runs from there to a
remote BA11, also with 2 SUs. A third cable runs back to the rack door/junction block
(labled "bus station", BTW) and finally a fourth cable runs to a small rack
mounted I/O box with a single SU and?an M9302 terminator in the last slot. Cable runs must
be about 20-25 feet total.
At first, I was worried that the length was too long (though it was a working system in
use for several years) but after a quick websearch
(www.psych.usyd.edu/pdp-11/unibus.html), I see that the bus can be up to FIFTY FEET before
a repeater is needed. My short term plan is to pull all the cables and move the 9302 into
the system box for testing. Now I'm worried that the bus might be too short - do I
need to look for one of the "new" jumpers with two feet of cable or should it
work with my old M9202 jumper block?
Jack
2 Feb
2 Feb
3:25 p.m.
From: "Jack Rubin" <jack.rubin at ameritech.net>
Sent: Tuesday, February 02, 2010 7:36 PM
To: <cctalk at classiccmp.org>
Subject: pdp11 bus - how long can it go?
As I slowly dig into "my" new 11/34A,
I'm amazed by the bus configuration.
Starting from the CPU, the main BA11 chassis has a double (9-slot) system
unit, joined to a single (4-slot) SU by an M9202 jumper. From the last
slot in the chassis, a Unibus cable runs to a junction block on the
cabinet back door. A second cable runs from there to a remote BA11, also
with 2 SUs. A third cable runs back to the rack door/junction block
(labled "bus station", BTW) and finally a fourth cable runs to a small
rack mounted I/O box with a single SU and an M9302 terminator in the last
slot. Cable runs must be about 20-25 feet total.
At first, I was worried that the length was too long (though it was a
working system in use for several years) but after a quick websearch
(www.psych.usyd.edu/pdp-11/unibus.html), I see that the bus can be up to
FIFTY FEET before a repeater is needed. My short term plan is to pull all
the cables and move the 9302 into the system box for testing. Now I'm
worried that the bus might be too short - do I need to look for one of the
"new" jumpers with two feet of cable or should it work with my old M9202
jumper block?
Jack
Hi Jack,
If I understand you correctly, you want to get the remote BA11 and I/O box
out of the loop.
The quickest way is to pull the BC11 cable from the last slot of the 4-slot
SU in the main BA11 chassis, and put the M9302 where the BC11 cable was.
That all.
If the 4-slot SU in the main BA11 box is further empty (not clear to me),
you can even get rid of that 4-slot SU too by pulling the bridging M9202 and
put the M9302 in the last slot of the 9-slot processor backplane.
The M920 jumper connects directly from the left to the right connector PCB,
it is the M9202 jumper block that actually has 2 feet of "BC11" cable
between the PCBs.
The M920 was used in the PDP-11/20 and 11/40 AFAIK. The M9202 is typically
found in the 11/34(A).
- Henk.
4 p.m.
We had an 11/45 ( as I recall) at the U of Illinois that was said to be the
longest unibus in the world. It had 2 DB11 repeaters on it, and there was
talk or putting on a third. I can't remember how many bus loads were on
there, but this sys was loaded.
Paul
On Tue, Feb 2, 2010 at 12:36 PM, Jack Rubin <jack.rubin at ameritech.net>wrote:
As I slowly dig into "my" new 11/34A,
I'm amazed by the bus configuration.
Starting from the CPU, the main BA11 chassis has a double (9-slot) system
unit, joined to a single (4-slot) SU by an M9202 jumper. From the last slot
in the chassis, a Unibus cable runs to a junction block on the cabinet back
door. A second cable runs from there to a remote BA11, also with 2 SUs. A
third cable runs back to the rack door/junction block (labled "bus station",
BTW) and finally a fourth cable runs to a small rack mounted I/O box with a
single SU and an M9302 terminator in the last slot. Cable runs must be about
20-25 feet total.
At first, I was worried that the length was too long (though it was a
working system in use for several years) but after a quick websearch (
www.psych.usyd.edu/pdp-11/unibus.html), I see that the bus can be up to
FIFTY FEET before a repeater is needed. My short term plan is to pull all
the cables and move the 9302 into the system box for testing. Now I'm
worried that the bus might be too short - do I need to look for one of the
"new" jumpers with two feet of cable or should it work with my old M9202
jumper block?
Jack
4:05 p.m.
In case you didn't know, the legnth of most DEC cables is usually in the -xx
after the part number. The unibus cable BC11A-10 is a ten foot cable. A
BNxxx-xx is usually in meters
Paul
On Tue, Feb 2, 2010 at 12:36 PM, Jack Rubin <jack.rubin at ameritech.net>wrote:
As I slowly dig into "my" new 11/34A,
I'm amazed by the bus configuration.
Starting from the CPU, the main BA11 chassis has a double (9-slot) system
unit, joined to a single (4-slot) SU by an M9202 jumper. From the last slot
in the chassis, a Unibus cable runs to a junction block on the cabinet back
door. A second cable runs from there to a remote BA11, also with 2 SUs. A
third cable runs back to the rack door/junction block (labled "bus station",
BTW) and finally a fourth cable runs to a small rack mounted I/O box with a
single SU and an M9302 terminator in the last slot. Cable runs must be about
20-25 feet total.
At first, I was worried that the length was too long (though it was a
working system in use for several years) but after a quick websearch (
www.psych.usyd.edu/pdp-11/unibus.html), I see that the bus can be up to
FIFTY FEET before a repeater is needed. My short term plan is to pull all
the cables and move the 9302 into the system box for testing. Now I'm
worried that the bus might be too short - do I need to look for one of the
"new" jumpers with two feet of cable or should it work with my old M9202
jumper block?
Jack
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henk.gooijen＠hotmail.com -
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