The M54649L consists of input circuit, control circuit, constant current circuit and output circuit. Two motors are connected to the IC; both of them are connected to output pin O1, and one is connected to output O2, and the other is connected to output O3. The motors are controlled by three input levels of input pins IN1 to IN3. As shown in the logic truth table, the control statuses of `forward rotation', `reverse rotation', `brake' and `OFF' are selectable.