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New PDP-8/E Acquisition

BitWiz

Experienced Member
Joined
Sep 7, 2021
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419
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Glen Ellyn, Iil
This is also posted in the PDP-8 google group. Please forgive me for any redundence.

I have recently acquired a running (I haven't received it yet so I don't know for sure) PDP-8/E and what looks to be a PC05 (I haven't actually received the system yet so I'm not sure).

The PDP-8/E comes with only one 20 slot H919 Omnibus back plane. I have previously acquired a separate H919 back plane which I would like to add to the PDP-8/E case.

The assembly drawing for the PDP-8/E calls for some kind of foam to be placed under the back plane. Does anyone know what I should use? Should it be conductive or just something to keep the pins from shorting to the case itself.

Does anyone know where I can buy, beg, borrow or steal a pair of M935 Omnibus Bridge sets?

The PCP-8/E has the following boards already installed:
M8330 Timing Board
M8310 Major Register Control
M8300 Major Register
M837 Extended Memory/Time Share Control
M8650 Asynchronous Data Control
W966 Wire Wrap Board (unknown circuit)
M840 High Speed paper tape reader/punch control
M849 RFI Shield
G104 4K Core Sense/Inhibit
H220 4K Core Stack
G227 4K Memory X/Y Driver
M8320 Bus Loads/Terminator

I will be adding an M848 Power fail board that I already have.

Does anyone know of a way to interface the PC05 to the M840?

Also, I am looking to acquire the following boards to add to the system:

More memory (core or semiconductor)
M8340 EAE Board 1
M8341 EAE Board 2
M868 TD8E DECTape Control
M8360 Data Break Interface
M8357 RX01 Controller
M7104 \
M7105 | RK05 Controller
M7106 /


Additional Hardware I would like to add. Most of this is just a dream because of lack of availability of the hardware and my limited budget.
M935 (I need a pair of these as soon as possible so I can add the second 20 slot backplane)
TU56 Dual DECTape Drive
RK05 Disk Drive
RX01 Dual Disk Drive
TC08 DECTape Controller
H960 Rack Cabinet w/PDP-8/E name plate preferably.
 
Welcome to the club! I wondered who'd bought that eBay listing ;)

The foam definitely shouldn't be conductive. I think it's mainly there for vibration prevention and to stop things getting between the PCB and chassis. It's not strictly necessary as there's enough of a gap there anyway unless you drop a screw under it.

The PC05 is meant to connect to a PDP-11 rather than an 8. The PDP-8 version is the PC04. There're quite different electrically but it should be possible to convert a PC05 to a PC04. IIRC the PC04 has an 8-slot backplane and the PC05 has 12 slots. Conversion would likely require wire-wrapping. The manuals should be on http://bitsavers.org/pdf/dec/papertape/

I don't personally have any of the cards of peripherals you're after going spare, but if you keep a look out you'll be able to find some more memory and an RX01 easily enough. You can make a replica of the M8357 with 7400 series chips from this design: https://github.com/Roland-Huisman/Digital_RX8E_M8357R.
Your quickest and cheapest option for memory is probably this: https://so-much-stuff.com/pdp8/32KOmnibus/32KOmnibus.php. I've got one myself and find the added bootloader option especially useful. Since it only uses a single slot, you probably won't need the extra backplane for a while. I have a 20 slot system with x2 serial, EAE, RX8E, TD8E, and RK8E; and still have 3 slots left.
 
Does anyone know of a way to interface the PC05 to the M840?

Also, I am looking to acquire the following boards to add to the system:

More memory (core or semiconductor)
M8340 EAE Board 1
M8341 EAE Board 2
M868 TD8E DECTape Control
M8360 Data Break Interface
M8357 RX01 Controller
M7104 \
M7105 | RK05 Controller
M7106 /


Additional Hardware I would like to add. Most of this is just a dream because of lack of availability of the hardware and my limited budget.
M935 (I need a pair of these as soon as possible so I can add the second 20 slot backplane)
TU56 Dual DECTape Drive
RK05 Disk Drive
RX01 Dual Disk Drive
TC08 DECTape Controller
H960 Rack Cabinet w/PDP-8/E name plate preferably.
I looked at this system as well. I suspect what you have is a PC04 reader punch. I was thinking I even saw that on one of the photos.

I am interested in that wire wrap card. I actually considered getting this system just because of the wire wrap card but came to my senses. When you get it take some photos of that card and post it in the What did I do to my PDP-8 thread. I could probably find something to trade for it.

Just a couple of comments.

The M8360 is the data break extension for posibus and you need the M8350 as well.

You will want to add at least another 4k of memory and a total of 12k will be required if you want to boot OS/8 off of DECtape using the TD8E controller. You only need 8k if you don't need to boot from the TD8E.

The TC08 is a lot better choice for DECtape than the TD8E but does require the M8350 and M8360 and posibus cables. You could get by with a total of 8k using this.

I wish you well in your search!
 
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Congratulations on your new acquisition and welcome to the club. I was a bit disappointed that the seller listed it as a package (including the PC04). I already have an 8/e but would've bid on the PC04.

The eBay listing specifically listed the paper tape reader/punch as a PC04 (which makes sense since it includes the PC8E/M840 interface) so there's no need to modify it.

There's some info on the M935's that may be helpful if you want to use Eagle CAD to make your own.

If you're going to add a TC08 (for a DECtape I presume), you'll need a M8350 Postive I/O intf as well as the M8360 Data break intf. I'd suggest trying for the TD8E / M868 instead unless you plan to add other Posibus devices that would make use of the M8350/M8360 cards. Too bad the near-mythical TC8E design (per Charlie Lasner) has been lost to antiquity.

Please let us know what the W966 was meant for (if you can figure it out).
 
I already have 2 M8350 Positive I/O bus interfaces from a prior purchase so all I need is the M8360 data break boards.

The reader/punch is specifically the PC11 which is a PC05 that was modified, I don't know how yet, to work with the M840. It came with spare M741, M7450 & M774 cards. I wonder if these boards were replaced with modified boards to make it work with the M840.

It also has the 12 slot back plane of the PC05 rather than the 8 slot back plane of the PC04.

According to the seller the W966 was used as some kind of parallel interface to control some external device.

I had forgotten that I only need 8K if have a TC08 instead of a TD8E. No matter what memory I have I want to keep one core set in the machine for historical purposes. Other wise old or new semiconductor memory is fine.

I have ordered a crystal and connectors to convert the M8650 from 110 baud current loop to RS-232.

I have taken the system apart (except for removing the power supply) and completely cleaned it and everything seems to be working except for the lower 6 address lights on the front panel (Please see a separate thread on that problem).

Thank you for the information on the RX01/RX02 controller. I would buy one of these replicas if they were available. The same goes for the 62256 based CMOS static ram boards with boot loader. Though I know how to solder (I built the PiDP-8 and 11). The time and cost of producing the circuit boards and assembling them is prohibitive to me. My wife likes to see the front of my head occasionally.

Thank you everyone for all of the information and help.

Mike
 
I figured out how the PC05 (labeled PC11 on the unit) works with the PC8E (M840). The M840 has been modified!

The biggest difference between the PC04 and the PC05 is for the PC04 a lot of the control logic is on the PC8E board and in the PC05 the logic is on the Reader/Punch.

That's why the PC04 has an 8 slot back plane and the PC05 has a 12 slot back plane. Once I get the console terminal working then I will work on the reader/punch.
 
Update on my new PDP8/e, 1 week after acquisition.

I took the PDP-8/E nearly completely apart (I left the power supply in the case) and cleaned it thoroughly.

I replaced all of the missing screws on the original back plane.
I installed the second back plane.

I ran a few preliminary hand toggled CPU and memory tests and it seems that the CPU and memory are working.
The lower six bits of the address on the front panel aren't working quite right yet.
I am in the process of ordering new bulbs for the front panel as I have 3 that are burned out. I stole the EMA bulbs to replace the burned out bulbs for now.

I installed the M848 Power Fail/Restart board and connected it to the power supply and tested its functionality.

I converted my current loop cable to be BC01V RS-232 compatible. Leave it to DEC to only number 40 pins of a 44 pin connector.
On the M8650 Asynchronous Board I replaced the 14.418 MHz crystal with a 19.6608 MHz crystal, moved the stop bit jumper to 1 stop bit and changed the baud rate to 2400 baud.
I have not yet removed the 0.047uF cap that is recommended to be removed.

I wrote a simple serial port echo back program and toggled it in and I am up and running at 2400 baud. Depending on what kind of terminal I can get or if i hook it up to a spare laptop I will increase the baud rate to at least 9,600 or maybe even up to 115,200 if i'm connecting to a PC.

My next step is to connect up the PC11 to the M840 controller. The M840 was modified to operate with the PC11 before I got the machine.

Now that I have the TTY running I need to find a binary image of Focal or Basic that I can run in 4K and download through the terminal program on my PC for now. Then I will punch a copy of it so that I can actually use the reader/punch.

I have about 1/3 of a box of paper tape so I need to get some more. I recall seeing a box or two on ebay.

Special thanks for Vince Slyngstad for all of his help.
 
You should be able to use Dave Gesswein's Dump/Restore programs to load Focal69. The link to his page is:https://www.pdp8online.com/index.shtml
I know there are binary image copiess of Focal69 floating around out there. He probably has one in one of those images. Good luck.
 
Now that I have the TTY running I need to find a binary image of Focal or Basic that I can run in 4K and download through the terminal program on my PC for now. Then I will punch a copy of it so that I can actually use the reader/punch.

I think this is Focal 1969:
http://svn.so-much-stuff.com/svn/trunk/pdp8/src/dec/dec-08-aja/dec-08-ajae-pb
https://so-much-stuff.com/pdp8/software/dec.php

I use Lyle's "gtty" to send the tape image to the PDP-8:
http://svn.so-much-stuff.com/svn/trunk/pdp8/gtty/

Special thanks for Vince Slyngstad for all of his help.

You are wlecome!

Vince
 
Additional Hardware I would like to add. Most of this is just a dream because of lack of availability of the hardware and my limited budget.
M935 (I need a pair of these as soon as possible so I can add the second 20 slot backplane)

OK, I got these working, so I guess I'm ready to talk about them.
IMG_20210915_175926191sm.jpg IMG_20210925_140113419sm.jpg
Basically, I repurposed some paddle cards I had made to create cables. The first photo shows the mechanical design -- basically the cards are held one inch apart with spacers. Since my spacers are M3 (metric), I can create spacing of 25 or 26 mm, but not the proper 25.4mm. I created a pair of each. They are a little difficult to insert/remove, but they do go in :).

The second shows them inside my 8/E, which has booted OS/8. You can see a bit of the RasPi 0W that runs Serialdisk in the photo. The cardboard boxes just cover the unused backplane slots in case some rubbish gets dropped in there.

There are 40 connections between each pair of cards (some are redundant), which I made with stripped bits of #22 solid hookup wire.

Vince
 

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I don't recognise that backplane. It's not a DEC H9191 Omnibus backplane. It looks like a new/custom design using ECS connectors? Impressive. What connects to the 40-pin connectors on the bottom side?
 
I don't recognize that backplane. It's not a DEC H9191 Omnibus backplane. It looks like a new/custom design using ECS connectors? Impressive. What connects to the 40-pin connectors on the bottom side?

I can't take any credit for the backplane. That's a "Diasonics Inc. Digital Backplane" 500-00442-01-52. 18 quad slots. It's just something I had lying around that's convenient for sticking stuff into for a photo. The edge connectors are 36 pins and press-fit into the backplane PCB in a surprisingly robust way.

My work is entirely the rather simple interface cards, which I originally meant to interface to ribbon cables or to braided CAT-V cables to create Posibus or Negibus cables. Here those are being abused to create a wide straight-through cable one inch long. The power pins are not connected (A2, B2), and I'm also relying on the Omnibus backplanes not to propagate the test pin signals in or out. Each paddle card assembly is used to connect C1-V1 and C2-V2 straight across the gap.

Vince
 
After passing the instruction test maindecs I loaded focal and:


CONGRATULATIONS!!
YOU HAVE SUCCESSFULLY LOADED 'FOCAL,1969' ON A PDP-8 COMPUTER.


SHALL I RETAIN LOG, EXP, ATN ?:NO

SHALL I RETAIN SINE, COSINE ?:NO

PROCEED.

*

That is, of course, after I remembered to set realterm to 7 bits.

My PDP-8/E can actually do something in 4K.
 
Congratulations. I have read that if Focal runs it's a good test of the system working properly.
 
I have demonstrated that running Focal is a good test, but it is not foolproof!

Please ensure you still run the MAINDECs in the correct order. These identify a few weird issues that running an application doesn’t test for...

Dave
 
Congratulations. I have read that if Focal runs it's a good test of the system working properly.

Necessary, but not sufficient. Just like being able to boot OS8 does not mean your CPU is working 100%.
Need to run the DEC MAINDECs to check all the nuances.
 
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I ran Instruction Test #1 & #2. When I tried to run the Random Addition test I gave up after letting it run for an hour (Switches 2 & 3 were up for continue on error and run continuous) but I didn't get any output so I loaded Focal to play around. I will run the complete maindec set as my work time allows.

Thank for the advice.
 
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