17 Jan
2023
17 Jan
'23
3:17 p.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
