SBC6120 PDP-8SBC6120 PDP-8
SBC6120/FP6120 Show & Tell

Some orientation for Bob Armstrong's beautiful PDP-8 recreation.

You may download this MP4 video for local playback with this link: "Deep Thought Show & Tell"
The SBC6120 / FP6120, my custom OS/8 boot sector, and “Toggle Toys”

After building three of Bob Armstrong's beautiful PDP-8 kits with front panels, it seemed to me that they needed something to do. At the top of my list was a high quality “blinking lights” program (so I wrote one called “Deep Thought”, but that's a topic for another page).

Sure, you could hook these machines up to a serial terminal or a terminal emulator, then boot, run and use the classic PDP-8 OS/8 operating system — and that's pretty cool. But you don't need, or even use, the front panel for that. So my focus was on having some fun with Bob's stunning front panel. I also wanted to brush up on my PDP-8 assembly language coding skills  . . . not that there's much demand for that these days! So I came up with the idea of “Toggle Toys”; programs specifically written to use the front panels of these systems.

My original idea was that the Toggle Toys would be small enough to be “toggled” into the machine's memory directly through the front panel. And they can be. But only a masochist would want to do that more than once. Since the HD6120 single-chip PDP-8 lacked a multiply instruction, I needed to provide an unsigned integer multiply subroutine to support the pseudo-random number generators used by both Toggle Toys. So the programs ended up being larger and longer than I originally planned. Okay, they're both less than 256 words long, but that's still a lot of toggling! (They also ended up being more feature rich, so I think it all worked out.) My solution to the overly long Toggle Toys, was the creation of a multi-boot sector for OS/8. This means that they only need to be entered once and are then immediately available anytime in the future.

The following pages provide some video demos where useful, along with the full PDP-8 source code and instructions to allow any owners of Bob Armstrong's SBC6120 & FP6120 to create a front panel multi-boot environment and install both “DeepThought” and “LightsOut.”

This ZIP file (352kb) contains all of the recently-written bits and pieces of
SBC6120 & FP6120 PDP-8 code for DeepThought, LightsOut, the custom OS/8
boot sector, and other PDP-8 code snippet utilities I created for this project.

GRC's PDP-8 Pages:
CLICK HERE to learn how YOU can acquire & build
one of these complete PDP-8 systems for yourself !!!

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Last Edit: Jan 27, 2016 at 18:08 (421.95 days ago)Viewed 9 times per day