11/70 panel - physical structure

Parent Category: Projects Category: PDP-11/70 console panel on USB Written by Administrator

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:



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.



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 ...



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.



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.