Why?
People connected them to webserver, or installed networked interfaces, or simply controlled them with massive parallel I/O cards.
I choosed a different approach: Connect the PDP-11/70 panel over USB to a PC.
This has several advantages:
- The panel can easily be connected not just to MS-Windows boxes, but also to MAC OS or Linuxes.
- You can carry the panel and a notebook with you and present it everywhere.
- The implemention is cheap, and pretty straight forward. No microcontroller or programmable logic chip is involved, you need just a solder iron and an standard USB to parallel interface unit.
- Perhaps nobody has done it so far.
However later I scrapped this project and connected the panel to a BlinkenBone setup.
Physical structure
One challenge for the interface was the 11/70 panels pin count: There are 34 outputs for the switches and 51 inputs for the LEDs, distributed onto three 40 pin Berg connectors. And this is a small console, compared with this one (2100+ lamps, 185 switches).
Unfortunately, my pdp-11/70 panel is missing the white front bezel. Now watch me doing a “lamp test” for you:
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Fine, no LEDs are broken at the moment (but one had to be replaced already).
To interface the 11/70 panel, I used an IOWarrior56 module from Code Mercenaries. This is a full USB speed device with 50 bidirectional input/output pins. The IOwarrior acts as an USB HID (human interface device) ... exactly right for the console panel.
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The IOwarrior56 is the green board to the left. To multiply the I/O pins from 56 to 85 (= 34+51) pins, I built a bus structure with two 32 bit output registers and one 34 bit input register sharing the same IOwarrior pins. 34 pins are data lines, and 3 lines are output/input latch enable lines.
The input register consists of five 74LS244 drivers (U1-U5), the output registers are built from seven 74LS373 latches (U10-U16). I used DIL packages, mounted everything on a hole matrix board and did much soldering by hand. The design is pretty timeless and could have been built 30 years ago ...
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Luckily DEC uses 40 pin Berg connectors and 40-wire flat ribbon cables for interconnection between panel and the KB11-C processor. These are exactly the 40-pin IDE cables used in older PCs.
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Soldering took two days. Sorting the connections made me half crazy, until I labled all components and made a detailed netlist. I didn’t cared too much about pin/register bit assignments, decoding is done in software.
If I ever repeat this, I will make a printed circuit board.