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pdp-8/a build from parts

L

Lou - N2MIY

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Joined
Apr 1, 2008
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Location
Albuquerque NM / Potomac MD
Along the lines of the 11/04 I built from parts a while back, I have started work on the building of an 8/a system. Again, with thanks to Tim for many useful parts, we had a good starting point.

Here is a photo of the jerry-rig on the bench : http://www.vintage-computer.com/vcforum/album.php?albumid=182&attachmentid=11833 Needless to say, everything has been through a thorough washing. I actually washed the G8018 in the sink after removing all the electrolytic caps. I let it dry for two weeks before powering it up. I also washed the backplane in the sink along with all chassis sheetmetal. I took the boxer fans apart (snap ring on the hub of the fan blade comes out) washed everything and regreased the sleeve bearings. Basically, everything has been washed except the power transformer.

At this point, the H9300 and G8018 power supply are working good. The M8315 processor had been tested earlier in the 8/e (yes, you can pull the M8300/10/30 out of an 8/e and put an 8/a processor in a quad height card extender and run it in an 8e chassis!). M8316 programmer's interface is working, but I have not tested the serial line. The M8317 extended memory controller and bootstrap is working since all 32kW of memory is accessable and the bootstrap does load into memory and start executing.

I had to build my own operator's console : http://www.vintage-computer.com/vcforum/album.php?albumid=182&attachmentid=11837

I was very lucky to find an ugly programmer's console. The cast metal cover is in bad shape and will need filling and painting. The plastic trim piece cleaned up ok. The membrane keys still have a good feel. The programmer's console had a problem, which I repaired.

Memory is the homemade SRAM memory that I made for the 8/e (borrowed). Since it's working well. I will make another one for this machine. http://www.vintage-computer.com/vcforum/album.php?albumid=182&attachmentid=11835. That is the next order of hardware business. The next order or software business is to run the 8/a diagnostics from emulated papertape (send the tape images from a PC) after I toggle in a simple echo test to make sure the console SLU works.

I have a "spare" RX8E that I will put in here for running OS/8 from RX01/2 eventually. The RL8A in the 8/e works really well. If hell freezes over and I ever find another one, I'll put it in here.

I'm not sure what this machine will be used for. It is small enough that I might keep it in the house. I could put it between the Decmate I VT278 and RX02 pedistal in this photo: http://www.vintage-computer.com/vcforum/album.php?albumid=43&attachmentid=2425 . Then with a switch box (already have it and cables) I could switch the 8/a or decmate to the RX02. I would use the VT278 as a terminal to the 8/a when I wanted to use a real 8, or just run the decmate to run decmate stuff (I have WPS for the decmate.)

Lou
 
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I'm going to start calling you the "8th Man"

:danceparty:
 
Okay, so I googled "8th Man". He was a Japanese comic book hero with a story remotely like our Steve Austin (the Six Million Dollar Man). We can rebuild him..... we have the technology!

Lou
 
Sorry... sometimes I forget that we dinosaurs need to explain our humor.

:headslap:
 
Lou - N2MIY said:
Okay, so I googled "8th Man". He was a Japanese comic book hero with a story remotely like our Steve Austin (the Six Million Dollar Man). We can rebuild him..... we have the technology!

Lou
Click to expand...
I am glad I was able to supply you with many valuable parts when I moved from Pa. Some day I will find another 8e.
 
Folks,

This afternoon I finished building another 62256 based omnibus 32kW SRAM memory. I built one once a few years ago in a rather crude fashion that ended up consuming two slots because of the height. The recent build was on a Douglas Electronics prototyping board and is only one slot deep. See the picture: http://www.vintage-computer.com/vcforum/album.php?albumid=182&attachmentid=12029 . There is an IC missing in the photo at the lower left that is a 74HC14 which I did not have at hand when I took the photo earlier (I had to go desolder one off a junk board.) A photo with both the original and the recent build is here: http://www.vintage-computer.com/vcforum/album.php?albumid=182&attachmentid=12027 .

This took me about 30 hours to build. I have it in the 8/e at the moment running the DHKMA memory exerciser. It's been running for about an hour with no problems. Before starting the exerciser, I did manually deposit and read, then booted OS/8 and ran Adventure.

The design is by CHD, and his website with this design is here: http://www.chdickman.com/pdp8/ . I highly recommend this design because it has a low parts count, is easy to build, and supports databreak operation. A 3.6V lithium battery lasts for 10 years and is a memory battery when the machine is off. This gives this memory the feel of core, since the data is retained at power off.

Next steps for the 8/a project involve cosmetics as I attempt to make my own version of those plastic clips with the plastic balls on posts that hold the front panels on.....

Lou
 
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Lou,

Nice work! Can you send specs/part number/source of the sockets you used. The photos aren't clear enough for me to see, but it looks like you're wire wrapping them from the component side of the board. I'm used to the long-tail sockets that extend 1/2" or more through the back of the board. These look much nicer and don't seem to require as much inter-board space. It's also a lot easier to keep track of the pins when you're not trying to figure them out backwards. I need to build a couple of these myself.

Thanks,
Jack
 
Jack,

There's nothing special about these sockets. They're standard cheap dip sockets. I used single row header pins as the wire wrap posts, just placed right next to the sockets. I noticed that Reinhard uses this construction technique also.

When I have space (depth), I'd prefer to use the long tail WW sockets.

If you build one of these yourself, be sure to use a 74HC14 for the 7414. That's the one hint that isn't on CHD's page. I had to use HC because the bus load was too great and data break operations would not work until I made that change. LS is fine for the rest.

Lou
 
Lou,

Makes sense. Which Douglas board did you use? I can't quite make out the p/n in your photo - looks like 9-DE-8 but not quite sure that their description matches your photo. Can you clarify?

Thanks,
Jack
 
Jack,

It was a 9-DE-8. Although the Douglass website still shows a variety of configurations, you'd need to call to find out what they really have left. If you call, ask for Chad. He is the guy who knows the DEC stuff there.

One other little warning. There is an error in the etch on the 9-DE-8. On A, B, and C, the pin that is usually +5V is incorrectly bussed with the 15V on D. I ground that etch off in the D area.

9-DE-8 was also made for 16 pin DIPs. I did some modifications to use the bigger 62256 and 74245. I used another piece of perfboard as a drilling template and added holes where needed and ground off some etch that was in the way. There is an "LSI area" at the top of the board, but I didn't want to triple the length of the wrap wire to get up there and back.

I don't know a darned thing about making PCBs, but this project is screaming for one. The parts are cheap and dead common. Everyone with an omnibus 8 would want to build one. I'm sure a PCB version could be completely soldered in under an hour!

Lou
 
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RL8A Bootstrap (In print, finally)

RL8A Bootstrap (In print, finally)

I am amazed that I have never found the RL8A bootstrap in print. The 8/e crashed last Sunday as I was exercising the new memory (whole other story - it was a bad 7483 on M8300. Fixed and back to normal). When I went to reboot, I thought my RX01 boot floppy had a problem. I always boot from that, then send the OS/8 BOOT command to boot from RL. I thought it was about time that I figure out how to boot the RL directly. But I could never find the RL8A bootstrap in print???

So, looked at the contents of the 8/a boot roms that contained the RL8A bootstrap. I extracted the following that works perfectly when fat-fingered in from the programmer's console and is started from location 0001 :

RL8A Bootstrap

Address Data
1 6600
2 7201
3 4027
4 1004
5 4027
6 6615
7 7002
10 7012
11 6615
12 0025
13 7004
14 6603
15 7325
16 4027
17 7332
20 6605
21 1026
22 6607
23 7327
24 4027
25 0377
26 7600
27 0000
30 6604
31 6601
32 5031
33 6617
34 5427
35 5001

Now it finally exists in print. It looks like it would even fit in an MI8E diode bootstrap loader.

Lou
 
Short RL Bootstrap procedure

Short RL Bootstrap procedure

At the risk of being slightly off-topic - I have posted the PDP-11 version somewhere (here at VCF) in the past, but can't find it. It always takes me days to re-locate this when I need it, so I thought it was worth capturing in a post since the topic has come up again, although in reference to a PDP-8.


In the back of the RL Training Handout (PDP-11 only), and my missing CPU Maintenance cards, and RL maintenance card ( PDP-11 and PDP-8 ) there are RL Bootstrap "procedures".


For PDP-11 it's a two instruction bootstrap, with some hand actions on the drive and at the console.
Code: 
11/34 RL BOOTSTRAP PROGRAM 

Ensure that the heads are over cylinder 0 and head 
0 is selected by releasing the LOAD switch, 
waiting for the LOAD indicator to light, then 
depressing the LOAD switch. After the drive is 
READY, initialize the controller with a system 
INITIALIZE. Perform a bit status clear. Load the 
following program into memory. 

LOC         CONTENTS        COMMENTS 
10000       012737          Load CSR 
10002       000014 
10004       174400 
10006       000001          Wait 



Start the program at 10000 and allow it to run for 
a few seconds. Halt the program and restart at 
00000.
This works on every PDP-11 I've tried it on.

Slightly longer in the PDP-8.
Code: 
RL8-A BOOTSTRAP

Ensure that the heads are over cylinder 0 and head 
0 is selected by releasing the LOAD switch, 
waiting for the LOAD indicator to light, then 
depressing the LOAD switch. 
Load the following program into memory.

LOC            Contents         Comments
21              7600               Clear AC and constant
22              6600               Clear RL8-a
23              7332               Generate constant
24              6605               Load SAR with 20
25              1021               Load constant into AC
26              6607               Load WC
27              7327               Generate constant
30              6604               Load CMD B
31              6601               Skip on Done
32              5031               Loop

Start program at 21. The OS-8 monitor will overlay this 
bootstrap.

Perhaps these additional options will prove useful as well.
 
Well, no more love for this 8/a for now. I've finished the restoration, and this 8/a will have to wait until I have the interest to put it in a rack with RX02 and RX8E. If I had another RL8A I would go that route too, but that might take a while. For now though, here is the finished unit: http://www.vintage-computer.com/vcforum/album.php?albumid=182&attachmentid=12366

It was warm enough to repaint the casting that encloses the operator's panel, so I finally did that and put it back together. Krylon "Satin Touch" Ivory Satin color is not too bad. Perhaps a little whiter than correct, but not bad.

Also, RSX11M+'s small RL8A bootstrap above does work. I tested it. Since I'm lazy, I'll be using the short bootstrap from now on!


Lou
 
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Lou - N2MIY said:
Well, no more love for this 8/a for now. I've finished the restoration, and this 8/a will have to wait until I have the interest to put it in a rack with RX02 and RX8E. If I had another RL8A I would go that route too, but that might take a while. For now though, here is the finished unit: http://www.vintage-computer.com/vcforum/album.php?albumid=182&attachmentid=12366

It was warm enough to repaint the casting that encloses the operator's panel, so I finally did that and put it back together. Krylon "Satin Touch" Ivory Satin color is not too bad. Perhaps a little whiter than correct, but not bad.

Also, RSX11M+'s small RL8A bootstrap above does work. I tested it. Since I'm lazy, I'll be using the short bootstrap from now on!


Lou
Click to expand...
Looks great. Excellent work.
 
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