Game Port - Hardware

Hardware

Unlike the TTL connectors used in the early days of home computing and game consoles (most notably the DE-9 connector originally found on the Atari VCS, which was the de facto standard on other systems) the game port is analog rather than digital, relying on some form of analog-to-digital converter (ADC) to interpret joystick movements. The typical implementation of a game port uses a capacitor and a simple voltage comparator, which together form a ramp-compare ADC, which needs to be periodically polled several times per second to provide a responsive game input.

The game port power can be loaded with approximately 750 mA; however, this is shared with the keyboard (max 100 mA), mouse (~ 25 mA), and the video port (VGA uses 50 mA), leaving approximately 575 mA for actual game port usage.

The game port uses a DA-15 connector and was originally usually mounted on a dedicated ISA card. Since the early 1990s, when the game port moved from dedicated expansion cards to PC I/O or sound cards, these connectors have usually doubled as connectors for MIDI instruments; two of the redundant +5V and GND pins of the original standard were rededicated to MIDI input and output to make this possible. To use a game port with MIDI instruments a cable is required with a male and a female DA-15 and two male 5-pin DIN connectors. The drivers and hardware for the game port midi capabilities are based around the now standard Roland MPU-401 MIDI interface (in UART mode only).