When I put for the first time my hands on a PlayStation, I liked very much the Sony controller. So I tried to find informations about the communication protocol between joypad and console. I found nothing.
So I borrowed an oscilloscope (my Zeroplus LAP-C arrived years later) and tried to reverse engineer the protocol.
This was a test program to help me in the reverse engineering, because the 2 channels of oscilloscope were not enough.
The program, with the aid of a simple hardware interface connected to then PC parallel port, can generate a data sequence on any output pins while reading and recording status of every controller signal