There are two buttons on the standard Amiga mouse. However, the control circuitry and software support up to three buttons. * The left button on the Amiga mouse is connected to CIAAPRA ($BFE001). Port 1 uses bit 6 and port 2 uses bit 7. A logic state of 1 means "switch open." A logic state of 0 means "switch closed." (See Appendix F for more information.) * Button 2 (right button on Amiga mouse) is connected to pin 9 of the controller ports , one of the proportional pins. See Digital Input/Output on the Controller Port for details. * Button 3, when used, is connected to pin 5, the other proportional controller input .