For making it easier to adapt Light Pens/Guns from other systems or new ones, we added a 4-pin connector to the board. The connections are labeled in the board as VCC (+5V), TR (Trigger), LS (Light Sensor) and GND.
Trigger (TR) = Request via output to port &FBFE. Light Sensor (LS) = CRTC Light Pen input.
Making the system compatible with [[Amstrad_Magnum_Phaser|Amstrad Magnum Phaser]] games, the most accuracy light gun system for CPC.