Parts:

• Adafruit ItsyBitsy RP2040 board, although almost any RP2040 board should work.
• MAX3233 or other 3.3v to RS232 Level shifter with two RX/TX pairs
• USB OTG Adapter
• Optional USB (Full Speed) Hub
• USB Keyboard & Mouse (Tested with Logitech K400+)

Connections:

• GPIO0 UART0 Keyboard -> VAX Keyboard Port Pin 4 / Alpha Pin 3
• GPIO1 UART0 Keyboard <- VAX Keyboard Port Pin 1 / Alpha Pin 2
• GPIO8 UART1 Mouse -> VAX Mouse Port Pin 2 / Alpha Pin 6
• GPIO9 UART1 Mouse <- VAX Mouse Port Pin 3 / Alpha Pin 7
• GPIO10 Piezo Buzzer for Keyclick & Bell
• GPIO11 Board LED (Adafruit ItsyBitsy RP2040)
• Ground - VAX Mouse Port Pin 1 / Alpha Pins 1,5,8,9,15
• +5V - VAX Mouse Port Pin 5 / Alpha Pin 13

VAX Keyboard Pinout is a RJ-9 with the pins up looking into the port Pin 1 is to the left. VAX Mouse Pinout is a MiniDIN-7. Alpha Pinout is given for using with a DEC 3000 M300x's D-SUB 15 Keyboard/Mouse connector.

Be aware that +/-12V are present on the mouse and keyboard connectors! You may need to connect the VAX Mouse Pin 7 to ground to tell the host computer/terminal a mouse is connected.

The foundations are in place to support the DEC Tablet protocol, but a TinyUSB driver would need to be written for the USB Tablet.