pluskb-protocol-analyzer

A protocol analyzer for Macintosh Plus/512k/128k keyboards.

HOWTO

Requirements

• PIC
  • Microchip MPASM (bundled with MPLAB)
    • Note that you must use MPLAB X version 5.35 or earlier or MPLAB 8 as later versions of MPLAB X have removed MPASM
  • A PIC12F1501 microcontroller
  • A device to program the PIC with
• Python
  • Python 3.x
  • PySerial

Steps

• Build the code using Microchip MPASM and download the result into a PIC12F1501.
• Connect the Tx line to a UART on a PC.
• Run the Python code.

Example

$ python3 -i analyzer-pluskb.py
>>> import serial
>>> KeyboardAnalyzer(serial.Serial(port='/dev/ttyS0', baudrate=115200, timeout=1)).run()

Serial Protocol

• Uses 8-N-1 at 115200 baud.
• Analyzer sends the keyboard bytes as received.
  • It is not possible for a third party observer on the bus to know whether the Macintosh or the keyboard is driving the data line.
    • The Python code infers this from the LSb of the bytes received (the keyboard sets it, the Macintosh clears it).
    • This does not cover some of the bytes sent on powerup.