Patent ID: 7418614

Claim:
An external signal detection circuit, comprising: an input port, to which a first end of a circuit including a pull-up resistor connected in series with a first switch portion and a second end of a circuit including a pull-down resistor connected in series with a second switch portion are connected, the input port receiving an input of an external signal; an input detection portion connected to the input port for receiving an input of the external signal and an input of an input detection signal that sets a timing for intermittently detecting the input of the external signal; a register setting portion connected to the first switch portion and the second switch portion, the register setting portion selecting either one of the first and second switch portions; and a connection control portion connected to the first switch portion and the second switch portion, the connection control portion controlling a connection time of either the first switch portion or the second switch portion, whichever is selected by the register setting portion based on an input detection signal detecting an input of the external signal to the input port and a control clock signal in synchronism with the input detection signal.