Embedded Learning Notes 8——Matrix Keyboard of 51 Single Chip Microcomputer-EEWORLD

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1. The independent keyboard is driven by an I/O port of the microcontroller. If the developed system needs to use many keys, in order to save I/O ports, we generally use a 4*4 keyboard, so that only one 8-bit I/O port is needed to drive 16 keyboards.

Embedded Learning Notes 8——Matrix Keyboard of 51 Single Chip Microcomputer

2. Key detection (detecting which key is pressed):

For the circuit in the figure above, first let P3 output 1111 0000, then start reading P3, according to the concept of line and, if one of P34~P37 is detected to be 0 (assuming P35 is 0), the column where the key is located can be determined; then conversely, P3 outputs 1101 1111 (the high bit keeps the value of the last detection), and also according to the concept of line and, if one of P30~P33 is detected to be 0 (assuming P30 is 0, then P3 is 1101 1110), the row where the key is located can be determined, thus determining the position of the pressed key. The entire detection time will definitely be less than the time it takes to press the key (about 20ms).

(Note: The concept of line AND - the high and low levels at both ends of the switch are ANDed, and the result is the level value of the entire line after the switch is closed)

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