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What did I do to my PDP-8 today.

DougIngraham

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Oct 2, 2019
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Rapid City, SD USA
I am starting a thread which I hope others will post to detailing what they did to their PDP-8(s). I steal this idea shamelessly from forums in some of my other hobbies. Feel free to talk about anything you have been working on as long as it is PDP-8 related. Software, hardware, restoration, maintenance, I am interested in all of it and what others are doing. And if I am interested in what you are doing, I am almost certain others are as well.

With that in mind I hope to see decent traffic here and I will follow up with my first post.

Doug
 

DougIngraham

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Oct 2, 2019
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Rapid City, SD USA
Today finds me working on my recently acquired DECmate II. (Yes, it is a PDP-8.) Really!

I have been collecting all the pieces to make a working machine and currently I am whitening the VR201 case by having it sit out in the sun. It has been exposed for several days so far and is quite a bit improved over the yellowish greenish color it had when I received it.

Also on the VR201 I am soaking the face of the monitor in plain water in order to dissolve the PVA holding the protective glass to the face of the vacuum tube. This isn't the worst case of cataracts I have seen but it is the first time I have had to deal with it. I am going to give it a week or two and if it doesn't just fall off I will go to plan B. I don't know what plan B is yet.

I dug out an old DOS machine, keyboard, monitor and hooked it up. Installed a 3.5 inch floppy as drive A: and a 5.25 inch 1.2 mb floppy as drive B:. Next problem was locating a version of DOS. I have hundreds of lbs of floppies but it is no longer in any kind of order. I eventually ran into a Win 95 boot disk which I remembered is sort of the last version of DOS. Plugged it in and it booted! YAY! You might be asking yourself why I needed a DOS machine and the answer is to run PUTR so I can burn some RX50 images to allow me to boot the DECmate. The next problem was how to get the data onto the 3.5 inch media. This turned out to be easier than I expected because while looking for a copy of DOS to boot I ran into a USB 3.5 inch drive (two of them actually) which I had never used. Got them from a friend years ago. Plugged it into my win 10 laptop and was able to look at the WIN 95 boot disk. Formatted a couple of 3.5 inch floppies and copied the PUTR files over to them and the image I needed. From this point it went like a champ. I will have to wait until I get a VR201 working to know if the DECmate can read it but PUTR seems to have no problems.

I think that is enough for today. I hope you found this of interest. Looking forward to hearing what you are doing!

Doug
 

commodorejohn

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Ah, I really need to get back to my -8 Roguelike project...there was no way I was gonna have it ready for VCF West, but since that plan was cancelled due to the apocalypse anyway, I guess I've got another year to get it done :lol:
 

tradde

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Katy, Tx
I too have a Decmate-II. Hard disk doens't work so it doesn't do much. The floppy drive in it seems to also have problems as it may click a few times but does not read. I'd like
to be able to create images for it too, but have no old DOS PC anymore. I may have to swap a floppy drive from another DEC machine I have to see if that helps. I have never
used a Decmate before. I prefer the blinken lights variety of 8, but sold my 8i and 8e long ago when I moved from Pa to NM. Best of luck to you.
 

DougIngraham

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I got this particular DECmate II from Vince Slyngstad. We were able to verify that it would boot from floppy using one of the WPS (Word Processing System?) diskettes. We weren't able to make a copy of this boot disk at the time and didn't know why but I think I understand why now. We did several things wrong, wrong media and we had write protected the destination floppy. I took it all apart a couple of weeks ago and cleaned out all the grime. I 3D printed new feet for it as the original rubber feet were almost completely gone and I couldn't find anything even close to the right shape, size or materials. At the moment I have a monitor which is soaking in water, an untested keyboard, and an untested spare RX50 drive. The keyboard is in what I would class as very good condition cosmetically so I am hoping it will work. The drive popped up on an EBay search and was a reasonable price and I was lucky enough to win it uncontested. I have a lot of appropriate media and I would be happy to make some images for you once I know they work. From my research I discovered that you need to use a 1.2 mb drive to write the image but you do not use the quad density media. The RX50 makes use of only one side but uses the 96 tracks per inch ability of the high density drive. It writes that single side at lower bit rates. A really oddball format. It is a little surprising that a DOS PC even with special software can handle it.

Doug
 

Mike_Z

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Hi Doug, good to here from you. I find that the weather is still too warm for computer work. Most of my time has been spent on old cars. Have been working on a 1913 Model T roadster that came from Newton Iowa. Lots of fun. BUT......I have been collecting old FORTRAN IV books. I want to re learn FORTRAN. It was the first language I used back in the late 60's. I have the DEC version of FORTRAN IV and have worked out a few easy programs. In fact last winter, I found a bad transistor on my EAE boards. The FORTRAN square root function, which uses the EAE was giving wrong answers. I also cheat a little Simh goes a lot faster than the PDP8e and the teletype. Hope it's not too hot in South Dakota. Mike.
 

daver2

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Hey Mike, long time no hear.

I thought it was ‘T’ weather for you :)!

It has been hot this side of the Pond recently as well. By the time we get AC installed the weather will change though!

Dave
 

DougIngraham

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Rapid City, SD USA
Hi Mike.

I am not familiar with the PDP 8/t variant of which you speak. Since the picture shows it being black it must have been some super secret project spawned deep in the Maynard skunkwerks. I am guessing it was some sort of autonomous vehicle control program in the 60's.

Simh and other emulators are a decent replacement as long as you run them on appropriate hardware. My own emulator should not be run on anything faster than an Intel 80386 33 mhz. Anything more modern than that is too fast. Simh is a little slower so it is probably ok to use one of the faster 80486 cpu's for that. I have estimated that modern servers are approximately 200000 times faster than the PDP-8 when using a single core.

On your EAE repair, did the EAE Maindecs help you diagnose the issue? I was looking at those a few years back and was struck by the way it was written. The author almost always does a CLA CMA followed by an AND to load the AC from memory instead of the usual TAD. The only reason I could think of for doing this was to avoid using the ADDer as much as possible. For the most part the EAE test would still work even with a somewhat broken adder. But of course you would never ever worry about the EAE not working if the ADDer was having issues.

Doug
 

Mike_Z

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This particular Model T is what is called a non electric car. There is no battery, just a magneto to power the ignition. Acytlene and oil power the lamps. So the PDP8 could fit in the car, but you would have to add some kind of power, maybe a wind turbine?

I use my Simh on my Windows 7 64 bit machine. I have seen no problems, in fact you are the first to mention such a thing. Now I have to go look.

Yes I used the MAINDEC as a starting place to trouble shoot the EAE. Do not remember exactly what the problem was, but i think it was some kind of division problem. I'd have to look at my notes to be sure. CRS is another problem with old humans. Mike
 

DougIngraham

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Rapid City, SD USA
This particular Model T is what is called a non electric car. There is no battery, just a magneto to power the ignition. Acytlene and oil power the lamps. So the PDP8 could fit in the car, but you would have to add some kind of power, maybe a wind turbine?

I use my Simh on my Windows 7 64 bit machine. I have seen no problems, in fact you are the first to mention such a thing. Now I have to go look.

A wind turbine would be interesting except for no power when not moving. In the DIYEV circles, mention of wind turbines is always followed by overunity issues the idea being you can charge the battery from the wind turbine while you drive down the road.

The only issue with using simh or other emulators is that they are too fast on computers faster than slow 486's or fast 386's.

Doug
 

tradde

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I wish now that I had not recycled my old Linux box. It most likely had a 5.25 floppy drive. Or one could have been added. Anything I have now
doesn't have any way to plug in a floppy disk to a controller. I have many blank floppies and would gladly send a few if you could make me
a bootable image. I should try to floppy drice from one of my other DEC systems, as those work. It may be I have bootable media but the
floppy in the Decmate doesns't wish to read it.
 

Roland Huisman

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Feel free to talk about anything you have been working on as long as it is PDP-8 related. Software, hardware, restoration, maintenance, I am interested in all of it and what others are doing. And if I am interested in what you are doing, I am almost certain others are as well.

Really nice idea! It seems that there are a lot of people having fun with these machines
but don't post anything about it. Maybe because they think it is not special, maybe they
don't want to put much time to make a posting, or maybe don't want to show their collection...?

The last PDP8 thing I did is build another TTL VC8E clone so all my Omnibus machines have the
graphics (SpaceWar!) capabilities. Since a few weeks I have also a PDP11/10, so four bits extra... Oh dear...
Recently I got some PDP8 paper tapes with some music software. So I want to see if I can
make an interface for that so I can run the music program. Would be fun to have a good
sound quality instead of that horrible AM radio sound...

I don't know how often you check the forum here. I have made a few (too much?) topics which
are PDP8 related. When you check out my postings you will see quite a lot PDP8 related stuff...
I made some clone boards from several Omnibus boards. I have shared them all on my GitHub.

A computer using tubes would be high on the wish list. But even a small hybrid machine like the LGP30
is not really suitable to handle at home. So I have some Anita calculators which are hybrid with diode/Tube logic
and diode/tube/transistor logic. Really fun to have a calculator with over 200 tubes in it :D

My fun is restoring and developing hardware. My biggest wish is to have a discrete computer
like the Straight 8 or a PDP8/S. Just because the beauty of the technique with discrete transistors...

Regards, Roland
 

m_thompson

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Jul 8, 2014
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Rhode Island, USA
So many PDP-8 related projects...

Finish getting P?S/8 running on the PDP-8/I at the RICM.

Paint the switches on my very early version of the PiPDP-8 and finish the assembly. Need to update the software to the latest version.

Repair and modify the really old EAE boards for the PDP-8/e and see if they can be made to work with the newer CPU boards.

Finish repairing the programmer's front panel for the PDP-8/a at the RICM. I need find a rattle can paint color that is close to the original color so I can repaint the metal part of the front panel. I need to repaint and reassemble both of my 8/a programmer's panels too.

Fix the power supply in my WT78 and see what else is broken. Get an RX01 working, installed in a desktop case, and connected to the WT78. Impress my wife by booting her decades old WPS diskettes and read her master's thesis. Get a LQP02 working and connected to the WT78.

Install the hex-serial board in my PDP-8/a #1 and get that working.

Repair the RK8E and an RK05 and add it to my 8/a #1.

Assemble PDP-8/a #2 from the pile of parts and boards.

Assemble PDP-8/e #2 from the pile of parts and boards.

Add a paper tape reader to my 8/e #1.

Install and test the VT8E boards in my 8/e #1, connect a composite monitor, and find a way to connect a parallel keyboard. Install the OS/8 drivers and have a really fast terminal.

And many more PDP-8 projects to do.
 

DougIngraham

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Oct 2, 2019
Messages
464
Location
Rapid City, SD USA
A computer using tubes would be high on the wish list. But even a small hybrid machine like the LGP30
is not really suitable to handle at home. So I have some Anita calculators which are hybrid with diode/Tube logic
and diode/tube/transistor logic. Really fun to have a calculator with over 200 tubes in it :D

My fun is restoring and developing hardware. My biggest wish is to have a discrete computer
like the Straight 8 or a PDP8/S. Just because the beauty of the technique with discrete transistors...

I think it is fine to post as much or as little as you like here. If you have a restoration thread elsewhere you might post a couple of lines here mentioning the progress and then a detailed posting on your main thread. My intention for this is to post little updates that don't need their own thread. But it is all good.

Tubes! That would be ambitious. I almost immediately get overwhelmed thinking of all the engineering issues you would need to overcome. The power and cooling issues would be difficult problems to overcome.

On the other hand it would not be all that difficult to make replica flipchip modules and wire up a Straight 8. My own version of this would be to design an 8 CPU using FETs instead of transistors.

My update on the DECmate is that I continued the sun bleaching of the case. Progress is slow but it looks quite a bit better. I need to take some photos.

I also researched VGA signals thinking I could rig up a cable from the DECmate to a VGA monitor but that is not really practical. The DECmate presents a composite monochrome NTSC like video signal but VGA wants separate horizontal and vertical sync signals. Those signals exist in the DECmate but I am not ready to try to bring them out of the machine. I do have the Sanyo monitor from my SOL-20 which accepts a composite signal so it might work to feed it into that. It is looking for interlaced video but it would probably still lock up and work. Something to think about.

Doug
 

daver2

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>>> On the other hand it would not be all that difficult to make replica flipchip modules and wire up a Straight 8. My own version of this would be to design an 8 CPU using FETs instead of transistors.

A while ago I had the very same thought.

Looked at getting some PCBs made using Vince's GERBER's - my problem was finding suitable PNP transistors. I was working on a SPICE model of the straight-8 at the time. I coded the schematics into EXCEL and wrote some VB to identify the errors in the schematics. It found a few. Only just (finally) got round to resolving all of the errors. I am now left with a load of unconnected flip-chip pins. These may (of course) be correct - so I will have to work through each flip-chip at a time looking at the individual gate usage to see if the unconnected pins should really be connected to something - or really left unconnected.

I have already modelled the individual flip-chips in SPICE, so the plan was to use EXCEL VB to generate the main logic linking all of the flip-chip sub-circuits together.

I also looked at a FET implementation - based upon an 8/e. I had originally coded a -8 up in LOGISIM and got that to work with the MAINDECS, Chess etc. I managed to get the main data paths (registers, adder etc.) done - but eventually broke LOGISIM! Too complex a project me thinks... Not bothered since to find another circuit simulator though.

Recently come across the EDDA3. This was a transistorised process control computer. Much simpler than the -8 but using relatively common (for the time) NPN transistors (e.g. BFY51, BSX52, 2N3055 etc.). Currently working on a SPICE implementation of that (one board every week at current progress).

I had some problems with the initial cycle generator logic, so what I learnt here regarding initial conditions in SPICE would have caused me issues with the SPICE straight-8 implementation anyhow. Useful learning...

Anyhow - not considering a transistorised -8 for many years (unless someone can find a large stock of suitable PNP transistors of course :))...

Dave
 

Mike_Z

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Well.... now you did it. You rekindled some interest in Fortran IV. I actually stayed up late to try some examples. I wanted to see what kind of error codes I would get if my program encountered an integer larger than what the DEC Fortran IV would handle.

Code:
.R EDIT
*TEST.FT<TEST.FT

#R

#L
10      I=10
20      WRITE(4,100)I
100     FORMAT(" MAX= ",I3)
        STOP
        END

#

All this program does is assign I =10 and then prints it out.

I found that the max integer for the DEC PDP8E Fortran IV is +/- 8,388,608. So I tried 10,000,000 for I and assembled it. The compiler did not report anything wrong, nor did the assembler or loader. Then when I ran it via FRTS, the program ran, but the out put was I=******. Anyway this is the kind of stuff I want to do with my PDP8E, but it will have to wait until the snow flies/ Mike
 

daver2

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Wait until the snow... It’s just too hot outside...

It is quite interesting what you have done. The implication being that the constant itself may be stored as text until it is actually required?

This would be unusual for a compiler...

I would expect that the compiler should have performed some form of semantic check on the source rather than just a syntax check so that an out-of-bounds check on a constant should have been flagged by the compiler rather than leave it to the runtime library.

Darn it, you’ve got me hooked now. Unfortunately, I have had to shut the machine down as we have now got a storm hit us!

Too hot, followed by thunder, lightening and rain...

Dave
 
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