An input device includes an input circuit including a plurality of key switches connected in parallel to one another, and a control circuit including a key input terminal to which a first terminal of the input circuit is connected, and an interrupt terminal to which a second terminal of the input circuit is connected. When a key switch is turned ON, an interrupt signal is input from the second terminal of the input circuit to the interrupt terminal, whereby the control circuit transitions from a power saving mode to a normal mode. Then, the control circuit determines which one of the key switches is turned ON based on a value of a voltage applied from the first terminal of the input circuit to the key input terminal. Thus, it is possible to realize a power saving mode without having to provide a comparator.
1. An input device, comprising:
an input circuit including a plurality of key switches; and
a control circuit including a key input terminal to which a first terminal of the input circuit is connected, and an interrupt terminal to which a second terminal of the input circuit is directly connected,
wherein when a key switch is turned ON, an interrupt signal is input from the second terminal of the input circuit to the interrupt terminal, so that the control circuit transitions from a power saving mode to a normal mode, and the control circuit determines which one of the key switches is turned ON based on a value of a voltage applied from the first terminal of the input circuit to the key input terminal;
the input circuit includes a plurality of voltage determination circuits connected in series with one another, each voltage determination circuit including a resistor and a key switch;
the first terminal is a connection node between the resistor and the key switch of a first voltage determination circuit, the first voltage determination circuit being one of the voltage determination circuits that is connected directly to an external power supply;
the second terminal is a connection node between the resistor and the key switch of one of the voltage determination circuits other than the first voltage determination circuit and a last voltage determination circuit, the last voltage determination circuit being one of the voltage determination circuits that is electrically farthest away from the external power supply;
the key switches of the voltage determination circuits that are subsequent to the second terminal are all non-mode-change key switches and if the non-mode-change key switch is turned ON, the interrupt signal is not input to the interrupt terminal; and
the key switches of the voltage determination circuits that precede the second terminal are all mode-change key switches and if the mode-change key switch is turned ON, the interrupt signal is input to the interrupt terminal.
2. An input device according to claim 1 , wherein:
the first terminal is at a predetermined voltage when the key switches are all OFF and at a voltage lower than the predetermined voltage when a key switch is ON; and
the second terminal is at the predetermined voltage when the key switches are all OFF or the non-mode-change key switch is ON, and at a low-level voltage being the interrupt signal when the mode-change key switch is ON.
3. An input device according to claim 1 , wherein an impedance of the interrupt terminal is higher than a combined impedance of the resistors of the input circuit.