Patent ID: 6538582
Filing Date: 2003-03-25
Classification: H03M

Abstract:
A key-pressing circuit used for encoding and decoding key-press position information of a keyed input device, the key-pressing circuit comprising:a control unit comprising a controlling port and a detecting port, the controlling port capable of being in either a grounded state or a floating state; a first charge storage circuit comprising a charging port that connects to the detecting port of the control unit; a key matrix circuit comprising a plurality of resistors and an associated plurality of switches, each of the resistors and each of the switches comprising a first end and a second end, the first end of each resistor connecting to the second end of its neighboring resistor so that the plurality of resistors forms a series resistor circuit that has a first end and a second end, the first end of each switch separately connecting to the second end of its associated resistor, the second end of each switch connecting to the controlling port of the control unit, the first end of the series resistor circuit connecting to the charging port of the first charge storage circuit; wherein when one of the switches is actuated and the controlling port is in the grounded state the first charge storage circuit will discharge, however when the controlling port is in the floating state the first charge storage circuit will recharge, the detecting port detects if the charging port of the first charge storage circuit reaches a predetermined voltage; wherein the control unit measures the time period from when the controlling port reached the grounded state till the detecting port detects the predetermined voltage, and the control unit determines the corresponding position of the actuated switch according to this time period.