As readers of my bLog will know, I have a soft spot for Digital Equipment Corporation's hardware. I'm the fortunate owner of multiple terminals and the PiDP-8 and PiDP-11 kits. At VCF Midwest this year I met a guy who explained to me about the RetroBrew Computers SBC6120 Single Board Computer built on the Harris 6120 Microprocessor. He had built one and had parts left for multiple kits. He sold me a complete kit with all the parts.
The documentation for this kit is very good. I'm glad that I read through the instructions before I started though because this is not a beginner's kit. And there are notes about the RBC revision of the board that you have to read which superceed the original documentation, so you need to go back and forth between the updated notes and the original detailed documentation. The traces on the board are very small and the advice about using a fine tip on the soldering iron and a fine solder was very helpful. My build went very well. I spent one afternoon doing the bulk of the soldering, then cleaned the board and set it aside. I came back the next day and did touch up soldering and more cleaning. I also spent time re-reading the "bring up" instructions and the jumper settings required.
I brought the board up in steps using the described procedure and it worked right away. I was very pleased that I'd gone slowly double checking the work along the way. I'm sure that taking my time ended up being less time and certainly less frustrating than troubleshooting a design that I'm not familiar with.
I'm in the enviable position of having to decide which terminal to pair with this system and since my VT100 is tied up with the PiDP-8 I went with the VT220. The documentation does point out that you need to use 7-M-1 in order to get the proper display from both the boot loader and from OS/8 after it starts.
There are three different disk images linked from the RBC page about the SBC6120. I used a Windows 10 computer to write these out to some small CF cards that I had on hand. At first I thought that my disk images were not working, however the root cause ended up being that I had not saved the serial settings in the terminal and when I cycled power it went back to 8-N-1. Once the serial settings were restored and saved to 7-M-1, I was able to get output from all three of the boot disk images linked above on the RBC page.
I'm quite happy to have one of these PDP-8s on a Chip, it should be a great learning platform for the platform and the OS/8 operating system. Perhaps someday I may even be able to own "Real PDP-8" hardware.
Let me know if you have any stories to share about this platform, or better yet join us on the Vintage Computer Forum and let us know "What did you do with your PDP-8 Today".
