Hi Mike,
Look at this site :
I found this info :
The MFX mouse port (RS232, 1200Baud) is used as a replacement for the graphics-pen of the Alpha-keyboard. (Supported protocols: Microsoft 2-button 3-Byte protocol, MouseSystems 3-button 5-Byte protocol, ...) Here, the MFX generates an output stream compatible with the Alpha-keyboard graphics-pen protocol.
Hope it helps.
Laurent.