Abstract: An interface circuit includes a general-purpose CPU configured to transmit a clock to a serial encoder with which bidirectional serial communication of clock synchronization type is to be performed, the CPU being configured to transmit and receive data to and from the serial encoder; and an additional circuit configured to detect a start bit of reception data transmitted from the serial encoder. The general-purpose CPU starts counting the number of bits of the reception data in response to a detection signal from the additional circuit, the detection signal indicating the detection of the start bit. The CPU stops transmitting the clock to the serial encoder upon completion of counting a predetermined number of bits of the reception data.

Abstract: An interface circuit includes a general-purpose CPU configured to transmit a clock to a serial encoder with which bidirectional serial communication of clock synchronization type is to be performed, the CPU being configured to transmit and receive data to and from the serial encoder; and an additional circuit configured to detect a start bit of reception data transmitted from the serial encoder. The general-purpose CPU starts counting the number of bits of the reception data in response to a detection signal from the additional circuit, the detection signal indicating the detection of the start bit. The CPU stops transmitting the clock to the serial encoder upon completion of counting a predetermined number of bits of the reception data.

Abstract: A pump off control method comprises detecting the speed of the induction motor and an instantaneous value of secondary current of the induction motor. Down stroke time in every cycle of the pump jack is detected. An average value of instantaneous values of the secondary current of the induction motor in the down stroke time in said every cycle is calculated. An average value reference of the secondary current of the induction motor to be compared with calculated average value of the instantaneous values of the secondary current of the induction motor is set. The calculated average value of the instantaneous values of the secondary current is compared with the average value reference after the down stroke end in each cycle. An occurence of pump off is detected if the calculated average value of the instantaneous values is greater than the average value reference.