Abstract: The serial communication device capable of reducing the load on the CPU is provided for a system using the serial communications such as the car navigation system. The attention is focused on the control method of the serial communication, in which a DMA controller is used for the data reception in the serial communication, and a number larger than the number of data received at a time is set in advance as the number of transfers of the receive DMA controller, and further, the function to generate the timeout interrupt when data is not received for a certain period is added to the serial interface, so that the serial communication can be controlled and performed without applying the load on the CPU.

Abstract: A bill validator is provided which comprises a rotator with a slit and being rotatably attached to the bill validator, the slit being capable of aligning with a passageway when the rotator is in an initial position; a driving device for rotating the rotator; and a validator control circuit for judging authenticity of the bill by outputs of detective sensors and for controlling the driving device. The validator control circuit produces outputs to operate the driving device and thereby to rotate the rotator so as to wind some pulling string connected to the bill around the rotator after the bill passes the slit of the rotator, and the circuit evaluates the rotation rate of the rotator, and detects the unauthorized pulling string.