PDP-11/70 panel on USB - physical structure

Parent Category: Projects Category: BlinkenBone physical PDP-11/70 panels Written by Administrator


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:


pdp1170panel usb front2

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.


pdp1170panel usb back

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 ...


pdp1170panel usb rasterboard front

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.


pdp1170panel usb rasterboard back

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.