17 Jan
2023
17 Jan
'23
5:39 a.m.
I am working to understand a TU56 in my possession that came from an
unknown environment. A connecting cable that came with it reads "PDP9" on
one end so I wondered if this is actually associated with the TU56 or just
sitting in the same box before the TU56 came to me. I have read here:
https://gunkies.org/wiki/TU56_DECtape_Transport
That one can have a TU56 with a M531 or a G742 to serve as a bus
converter. THe M531 is for situations where one has a negative logic
controller and the G742 is for when one has a positive logic controller.
Jumping a few steps ahead, if the TU56 was attached to a PDP-9, would it
use a G742 if one tried to attach a TU56 to it? I feel as if the G742
would be used if the TU56 was intended for a PDP8 and not a PDP11, right?
I searched the web and will continue to research but I thought I'd ask
experts here. No, I don't use ChatGPT.
Bill
17 Jan
17 Jan
7:17 a.m.
On Tue, Jan 17, 2023 at 8:39 AM Bill Degnan <billdegnan(a)gmail.com> wrote:
I am working to understand a TU56 in my possession
that came from an
unknown environment. A connecting cable that came with it reads "PDP9" on
one end so I wondered if this is actually associated with the TU56 or just
sitting in the same box before the TU56 came to me. I have read here:
https://gunkies.org/wiki/TU56_DECtape_Transport
That one can have a TU56 with a M531 or a G742 to serve as a bus
converter. THe M531 is for situations where one has a negative logic
controller and the G742 is for when one has a positive logic controller.
Jumping a few steps ahead, if the TU56 was attached to a PDP-9, would it
use a G742 if one tried to attach a TU56 to it? I feel as if the G742
would be used if the TU56 was intended for a PDP8 and not a PDP11, right?
I searched the web and will continue to research but I thought I'd ask
experts here. No, I don't use ChatGPT.
Bill
First of all, here is a set of pre-restoration pics of the TU56 I am
cleaning up and trying to understand:
https://www.vintagecomputer.net/digital/TU56/index.cfm?sort=name&order=…
I found a good general description of how the negative / positive relates
to the PDP-8 and how peripherals fit into the picture.
https://homepage.cs.uiowa.edu/~dwjones/pdp8/models/
"The "negibus" or negative logic I/O bus used -3 and 0 volt logic levels in
92 ohm coaxial cable" - a M531 would be used if attaching to a computer
with a negative bus. A G742 indicates the computer using the TU56 had some
form of positive logic bus.
The positive I/O bus, or posibus, was a 100 ohm bus clamped between 0 and 3
volts with TTL drivers and receivers.
BUT - The cable that connects the TU56 to the external peripheral possibly
appears to convert the posibus to a negibus as well as data. So I am
thinking the presence of a G742 does not alone indicate the computer using
the TU56. Note the 18 connectors:
https://www.vintagecomputer.net/digital/TU56/TU56_PDP9-connector.png
I think a PDP-9 and earlier PDP8's were negative logic computers, so it's
possible that this TU56 was used with a negative logic computer, the PDP-9
despite the G742, given
1) The 18-pin bus adapter-ing on the other end of the TU56 positive bus
2) THe "PDP9" printed on the adapter.
3) The other side of the cable reads "TC02 E&F" (I believe).
I know PDP-9's attached to TU55's, but the TU56 was not invented yet.
TC02?
http://www.bitsavers.org/www.computer.museum.uq.edu.au/pdf/DEC-00-HRTC-D%20…
See page 22
(1) For a TU56M or TU56MH Transport: controller-to-transport information
cable = 70-06412, transport-totransport (other TU56 or TU56H in system)
information cable = 74-5152. See Note 2 for TU56M or TU56MH connected to a
TD8/e Controller. (2) When a TU56M or TU56MH is connected to a TDa TD8/e
Controller, only one 70-08447 cable is used for both commands and
information. This cable has both a single-height and a double-height
connector module on the termination end. Insert the single-height connector
into slots A061 A07 and the double-height connector into slots AB 1 01 AB I
I.
Bill
12:02 p.m.
On Tue, Jan 17, 2023 at 10:17 AM Bill Degnan <billdegnan(a)gmail.com> wrote:
On Tue, Jan 17, 2023 at 8:39 AM Bill Degnan
<billdegnan(a)gmail.com> wrote:
I am working to understand a TU56 in my
possession that came from an
unknown environment. A connecting cable that came with it reads "PDP9" on
one end so I wondered if this is actually associated with the TU56 or just
sitting in the same box before the TU56 came to me. I have read here:
https://gunkies.org/wiki/TU56_DECtape_Transport
That one can have a TU56 with a M531 or a G742 to serve as a bus
converter. THe M531 is for situations where one has a negative logic
controller and the G742 is for when one has a positive logic controller.
Jumping a few steps ahead, if the TU56 was attached to a PDP-9, would it
use a G742 if one tried to attach a TU56 to it? I feel as if the G742
would be used if the TU56 was intended for a PDP8 and not a PDP11, right?
I searched the web and will continue to research but I thought I'd ask
experts here. No, I don't use ChatGPT.
Bill
<snip>
I consolidated my findings here:
https://vintagecomputer.net/browse_thread.cfm?id=788
Basically think that the TU56 can connect to a PDP-9 as long as the correct
bus connector is used. There is documentation how to attach a PDP-9 to a
TU55, which should be the same as the TU56 where it counts in this
situation. Because the 9 is a negative logic system, a M531 would be used
to connect with a (not sure PN) cable OR you'd use a G742 bus connector and
a W850 adapter + cable.
So yes, it's possible that my TU56 was attached to a PDP-9 on the other
end, at least for some period of time.
Bill
1:51 p.m.
On Jan 17, 2023, at 10:17 AM, Bill Degnan via cctalk
<cctalk(a)classiccmp.org> wrote:
...
I found a good general description of how the negative / positive relates
to the PDP-8 and how peripherals fit into the picture.
https://homepage.cs.uiowa.edu/~dwjones/pdp8/models/
"The "negibus" or negative logic I/O bus used -3 and 0 volt logic levels
in
92 ohm coaxial cable" - a M531 would be used if attaching to a computer
with a negative bus. A G742 indicates the computer using the TU56 had some
form of positive logic bus.
The positive I/O bus, or posibus, was a 100 ohm bus clamped between 0 and 3
volts with TTL drivers and receivers.
Interesting to see the terms positive and negative logic used this way. I'm used to a
different usage, where "negative" logic simply means the lower (less positive)
voltage is used to represent the boolean value "true" (1) rather than
"false" (0) as it does for "positive" logic. For example, the CDC
6000 series machines are "negative logic" in that sense: they represent boolean
true as 0 volts and boolean false as +6 volts.
paul
1022
days inactive
1022
days old
3 comments
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Paul Koning