| 摘要 |
PURPOSE: A circuit and a method for a key pad using an encoder are provided to reduce a size of a circuit by recognizing a key value of a key pad using an encoder, to save electricity consumption for operating a circuit by reducing the number of an element used for forming the circuit, and to increase an operation execution speed relevant to an input of the key by simply forming the circuit. CONSTITUTION: A user selects a key pad to execute a predetermined operation. An encoder(20) connects to a row and a column of each key and enciphers a key value. A latch circuit(40) inputs an input signal of the encoder(20) and transmits data to a CPU. The CPU recognizes the key value through the signal inputted from the latch circuit(40) and execute the operation. 5,6 columns of the key pad connect to an input voltage through resistances(R1,R2). An anode of diodes(D1,D2) is connected between 1,2 columns of the key pad and an input terminal of the encoder(20). Two diodes(D1,D2) get an input of an AND gate(23). An output of the AND gate(23) gets to an input of a FF(30). An output of the FF(30) connects to the input terminal of the latch circuit(40). A DA terminal of the encoder(20) connects to the first invertor(25). An output terminal of the first invertor(25) connects to a LE terminal of the latch circuit(40) and a key interrupt terminal of the CPU. An output of the first invertor(25) connects to an OE terminal of the encoder(20). An output of the second invertor(26) connects to a clock terminal of the FF(30). An additional circuit comprises the FF(30) and an AND gate(35) which inputs the output of the FF(30). An output of the AND gate(35) is outputted through a variable resistance(VR1). The encoder(20) is 16 keys encoder. The key pad circuit expanded for recognizing 24 keys is composed by adding the resistances(R1,R2) and the diodes(D1,D2) and connecting to rows of the key pad.
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