Abstract: In some examples, a hysteresis comparator includes a series resistor portion including a plurality of resistors for dividing a power supply voltage, the series resistor portion generating a first midpoint voltage and a second midpoint voltage higher than the first midpoint voltage, a first comparator configured to compare the first midpoint voltage and a reference voltage, a second comparator configured to compare the second midpoint voltage and the reference voltage, and a flip-flop having a clock terminal to which an output signal of the first comparator is applied and a reset terminal to which an output signal of the second comparator is applied. In some examples, a hysteresis comparator further includes an OR gate to which output signals of the first comparator and the second comparator are applied, and an AND gate to which output signals of the first comparator and the second comparator are applied.

Abstract: In some preferred embodiments, in an authentication system including a plurality of portable devices and a base station, if the portable device is operated by an internal battery, ID data encrypted at a higher level are exchanged (normal mode), and if the portable device is operated by electromagnetic induction coupling with the base station, ID data encrypted at a lower level are exchanged (backup mode). These two communication modes are performed in the same communication device. The portable device transmits a signal showing a state of the battery voltage to the base station, and the portable device and the base station store the battery state in the respective storing portions. At the time of initiating communication, the portable device transmits a signal in the normal mode as first communication.

Abstract: In some examples, a hysteresis comparator includes a series resistor portion including a plurality of resistors for dividing a power supply voltage, the series resistor portion generating a first midpoint voltage and a second midpoint voltage higher than the first midpoint voltage, a first comparator configured to compare the first midpoint voltage and a reference voltage, a second comparator configured to compare the second midpoint voltage and the reference voltage, and a flip-flop having a clock terminal to which an output signal of the first comparator is applied and a reset terminal to which an output signal of the second comparator is applied. In some examples, a hysteresis comparator further includes an OR gate to which output signals of the first comparator and the second comparator are applied, and an AND gate to which output signals of the first comparator and the second comparator are applied.

Abstract: A keyless entry system comprising a transmitter and a receiver. The transmitter increases a first number stored in the volatile memory according to rules, and transmits the first number by radio. The receiver receives the first number, and if the first number is greater than a second number stored in a memory, outputs a signal to indicate being authenticated as correct and updates the second number to the first number. Further, each time increase in the first number becomes a multiple of a predetermined number, the transmitter writes into a non-volatile memory a third number equal to the predetermined number plus the first number. When the first number in the volatile memory is erased due to the exchange, etc., of the battery, the transmitter reads out the third number from the non-volatile memory and writes the third number as the first number into the volatile memory.