The device is capable of functioning in four distinct, selectable communications modes: PS/2, RS232, GPIO (General-purpose I/O), and USB. The communications mode determines the functionality of the two special serial communications pins (PB6 and PB7). The device is placed in the required mode when firmware sets the specified mode bit in the communications control register. The firmware interface is similar in all modes. The same buffer area in RAM will accept the data to be transmitted. Up to 8 bytes may be loaded, and the data will actually be transmitted as soon as the appropriate command is issued (setting In Packet Ready in USB mode, for example).