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PDP-11/Hack de luxe

cbscpe

cbscpe

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Apr 11, 2017
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Switzerland
Not really satisfied with my breadboard attempt to build another PDP-11/Hack and also because I wanted to investigate a little bit more how the DCJ11 really works I decided to make another PDP-11/Hack. So I designed a Eurocard DCJ11 based Singleboard Computer. The PCBs arrived today and so nothing better then set them to use. But this time the PDP-11/Hack comes with an expansion slot. So with a proper PCB and the option to expand the SBC it has now become a "PDP11/Hack de luxe"
Here is a picture of the recently built unit

IMG_9539.jpeg
It is still a prototype and as expected already required an ECO. But not to bad for a start. If you ask what is this cable attached to the right, this is a USB to Serial/TTL adapter that connects to the console. As the complete computer draws less than 200mA the adapter also provides power via USB. And below the output of the mandatory PDP-11/Hack test program.

IMG_9541.jpeg
Sorry for the bad picture of the screenshot, but I think you get the idea. As a change of pace I used a real DC319 as the UART. The SBC only uses TH ICs. SMD parts are only used for the capacitors and resistors. Also I only used standard TTL logic. Byte writes are decoded properly, Power-Up is decoded and the 74HCT541 provides a defined power-up configuration and it comes with a reset button and a reset logic as well.

Cheers

Peter
 
Thanks for sharing!

This is very cool and def way cleaner than with the tons of jumbled wires ;-)
 
Cool stuff (y)
I have a few remarks, but maybe they are completely misplaced.
  1. I do not see a jumper to disconnect the 5V for power supply via USB. Maybe additions pop up in the future, taking the current over 500 mA. Then the USB power supply should be disconnected and ower has to be connected directly to the board.
  2. Looking at the space available on the board, why did you go for SMD resistors and capacitors? There are a lot of "old guys" in the PDP-11 community with eyesight no longer that of a youngster. IMHO, there is sufficient space for "normal" Rs and Cs (more in line with the old tech stuff).
  3. Why did you choose an card-edge type of connector? Something similar to DIN41612 (as used in VME systems) would be more reliable. Further, would it not make sense to have that connector at the edge of the board?
You probably had good reasons for the choices you made. Just curious ...
 
Henk said:
I do not see a jumper to disconnect the 5V for power supply via USB. Maybe additions pop up in the future, taking the current over 500 mA. Then the USB power supply should be disconnected and ower has to be connected directly to the board.
Click to expand...
Or a diode would work without risking forgetting to remove the jumper, though you would get the voltage drop which might cause issues.

CW
 
Henk said:
Cool stuff (y)
I have a few remarks, but maybe they are completely misplaced.
  1. I do not see a jumper to disconnect the 5V for power supply via USB. Maybe additions pop up in the future, taking the current over 500 mA. Then the USB power supply should be disconnected and ower has to be connected directly to the board.
  2. Looking at the space available on the board, why did you go for SMD resistors and capacitors? There are a lot of "old guys" in the PDP-11 community with eyesight no longer that of a youngster. IMHO, there is sufficient space for "normal" Rs and Cs (more in line with the old tech stuff).
  3. Why did you choose an card-edge type of connector? Something similar to DIN41612 (as used in VME systems) would be more reliable. Further, would it not make sense to have that connector at the edge of the board?
You probably had good reasons for the choices you made. Just curious ...
Click to expand...
As mentioned this is just a prototype, a draft so to speak, and it served as the learning piece for KiCad. I got impatient and wanted to get a working sample before every detail was honed to perfection. There will be a final version and more info on my homepage.
  1. Indeed, normally I put a zero Ohm resistor, but here I forgot. My bad :oops: . The final version will have a place to put a jumper/wire/resistor/diode.
  2. Here I don't agree. Being an "old guy" myself and having problems with my eyesight I'm still using a lot of SMD stuff. When it comes to 0.5mm pitch stuff I use a lamp with magnifying glass or the microscope. In my experience 0805 sized SMD resistors and capacitors are as easy to solder as TH equivalents. With TH components you always have to bend the wires and cut them later and you always need to turn around the PCB. SMD parts help you to save time. The goal was not to be in line with old tech stuff, but honestly SMD capacitors and resistors are pretty much in line with the era of the DCJ11. And in case you really have problems soldering SMD, you can always order the PCB with the SMD parts assembled. Problem solved.
  3. The card-edge decision was a cost based decision. This SBC will serve as the base for tests and experiments I have in mind. As a result there will be many expansion boards built just for the purpose to answer one or two questions I have.
Here some points from my planned to-do list
  • Use a GAL instead of the six TTL logic devices. That's the reason I did use sockets for them so I can remove them and put an expansion card with a GAL22V10 on it. I recently learned that ATF22V10C can be programmed by some cheap programmers. This is rather a nostalgic project. I used GALs some decades ago and in the last years was mostly using CPLDs, but many times a CPLD is pure overkill and the ATF22V10C has the advantage that they are available in PDIP-24 packages. And certainly matching the era of the DCJ11. The goal is to write some sort of primer in how to use GALs.
  • I'm aware that not everybody has a DC319. I only know of one offer on ebay where you can buy them and you need to buy at least a tube with 11 pieces. But in fact when you look at the price per piece they are very inexpensive. The CDP6402 and it's pin replaceable companions are much easier to get and you can buy just one. So another expansion board will use a CDP6402 and some glue logic for those that don't have DC319 but have a CDP6402.
  • For another project I need to test how the DV signal works in detail.
  • I want to fully understand power-fail
  • And then there is that piece de resistance, an expansion board that turns this SBC into a PDP-11 able to run RT-11.

I hope that explains your concerns.

Cheers

Peter
 
Peter,

Once you have all of the kinks worked out have you considered making a kit for those of us who would like to have an 11 that is a little bigger than a Pi😁.

Thanks,

Mike
 
Hi Mike,

I will certainly publish everything, but providing kits I donˋt think so ;).

Cheers

Peter
 
I was only making remarks, definitely no criticisim. I did not make a remark on those 6 TTL ICs, but I actually did think of one or two GALs replacing them :)
Might make routing simpler as well. 0805 SMD I can handle, but it's just that I prefer TH components.
Anyway, you have a cool project on your hands, and I will be following it (y)
 
No problem. As for the 6 TTL ICs, yes one GAL16V8 would easily replace them. I was in fact thinking to replace the 6 TTL ICs with a GAL16V8 for the final version. But one of the primary goal of the PDP-11/Hack is, that it can be built without the need of programming devices. So anybody with decent solder skills, a DCJ11 and a DC319 should be able to build it. I will be using GALs and CPLDs for the planned expansion cards.
 
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