Here is a description of the intellimouse protocol that I wrote up a while ago. An excellent page for mouse protocols can be found {{[jump="http://www.microsoft.com/whdc/device/input/mcompat.mspx"] here}} also. If you want info about imps2, here is what I have. It is straight out of the XFree sources, I have used it many times and it seems reliable : To initialize a mouse in imps2 mode, you send it 243, 200, 243, 100, 243, 80. Before that you have to initialize it as a PS2 mouse, though. The packet format is 4 bytes : P3: Byte 0: !block table Bit Contents 0 Left button 1 Right button 2 Middle button 3 Nothing? always 1 4 X bit 8 5 Y bit 8 6 Button 4 (untested) other sources say X overflow 7 Button 5 (untested) other sources say Y overflow !endblock Note that GPM currently expects buttons 4 and 5 to be unpressed or it will discard the packet. I have never personally seen a mouse that has these buttons. P3: Byte 1: X bits 7 to 0 X is calculated by : if (byte[0] & 0x10) byte[1] else byte[1] - 256; P3: Byte 2: Y bits 7 to 0 Y is given by if (byte[0] & 0x20) -byte[2] else 256 - byte[2]; P3: Byte 3: Z Axis (the roller). Indicates how much the roller has moved. I have never seen values other than -1 and +1 on a standard intellimouse. On my trust intellimouse with two rollers, I seem to remember that the second roller sends -2 and +2 in this field.