ekijak@ARDC.ARPA (Edmund S. Kijak, POINT) (10/03/85)
The four joystick ports are connected to two 6520 PIA (Peripheral Interface Adaptor) chips. Each bit of these ports can be set independently by software to be either an output or an input, then can be written to or read from. Specs for the 6520 can be gotten from Rockwell or Synertek. Each joystick port also contain pins for a pair of paddles. These are variable resistors. You can connect variable resistance sensors here and read them by software. Details are in the Atari Hardware Manual, or check old issues of Byte and other mags (around 1982, 1983).