The IO Expander is working and blinking the built-in LEDs!

Oh, and I wove the core memory too!

The first demo sketch will be in the basic Arduino environment, with the I2C Wire Library, and directly reading/writing to the registers of the MCP23017 IO Expander. At the moment, I'm testing the prototype Core4 with another prototype, a simple inline SAO with an RP2040-Zero. This little board will draw power from a host SAO (or USB C port) and pass the power up to the SAO plugging into the top. The RP2040 is also connected to the TOP SAO port I2C and GPIO1&2 lines.

Next step, control all the IO to write some core memory!