Progress: Building an I2C Bridge for the PiDP8i

[Heinz-Bernd Eggenstein]

Since today is Halloween, here's a Pumpkin-themed visual demonstration of the I²C bridge pseudo device for SIMH in PiDP8i that I'm working on.

https://youtu.be/hhU2XqalVmI

Not that this is useful as such, but it demonstrates a few of the features and also exposes some of the things that still need to be solved.

This planned extension of the PiDP8i software allows you to offload the processing of certain, configurable , IOT instructions to one or more I²C peripherals that you can connect to your PiDP-8i, typically this is intended for cheap microcontrollers like the RaspberryPi Pico. Those microcontrollers are then used to implement the input/output  logic that you want to control via the PDP-8.

This demo simulates

- An Analog-to-Digital Converter (ADC) for reading out a joystick 

- An ADC-channel multiplexer (three channels) for selecting the joystick axis

- two sets of 12 LEDs for effects (I should have used shift registers instead of individual GPIO lines per LED  which makes a total mess of wires....)

This could have been done by a single Raspberry Pi Pico but the demo uses two just to test the ability to talk to more than one I²C device. One was programmed in MicroPython for simplicity, the other in C for speed.

There are still a few limitations and open questions, more about that later, but I think this could be a fun thing to play with.

P.S.: Kudos to Steven Stallion whose libi2cd library is used in this project. Check out his PDP-11 I/O expander on Tindie if you also have a PiDP-11!

Happy Halloween.

HB