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Single-chip human-computer interaction--matrix key

2022-08-11 00:34:00 【an520_】

The key is a normally open push button switch,The common connection method with the single-chip microcomputer is shown in the figure.The two contacts open when the key is not pressed,单片机I/O口输入高电平;当按键闭合时,I/O口输入低电平.

一、button explanation

当I/O口为P0口时,由于没有内部上拉电阻,Therefore, an external pull-up resistor is required,当I/O口为P1、P2和P3口时,Because of the internal pull-up resistor,Therefore, the external pull-up resistor can be omitted.

二、按键消抖

The keyboards used in the single-chip system are all mechanical elastic keys,Because of the elastic effect of mechanical contacts,Jitter occurs at the moment when the key is closed and released,如图所示.Keystroke jitter generally persists5~10ms,In order for a keypress to be processed only once,Keystroke jitter must be eliminated.To eliminate key jitter, software debounce or hardware debounce can be used.

Software debounce refers to when it detects that a key is closed,Check again after a short delay,If key closure is still detected,The button is considered to be truly closed.

Hardware debounce method

1.R-S触发器

一旦有键按下,The trigger reverses immediately,The jitter of the contacts will no longer affect the output,The same is true when the key is released.

2.电容滤波

Connect a capacitor in parallel across the buttons,Take advantage of the time-delay characteristics of capacitor discharge,The jittering level is absorbed by the capacitor,So as to achieve the effect of anti-vibration;

三、独立按键

Independent keyboard means that each key occupies an independent pin.

四、矩阵按键

All keys on the same row are connected to one pin,All keys on the same column are connected to one pin.

（1）Column scan method

All row lines output high level,The column lines output low level in turn;Query the value on the row of this column,若为0,It means that the button on the row is pressed;If all rows on this column have the value 1,Then the query for the next column row value is performed;循环往复.

（2）反转法

All row lines are output0,Query the value on the column line,If the value on a column line is 0,It means that the button on the line is pressed;Then all column lines are output0,Query the value on the row line,If the value on a line is 0,It means that the button on the line is pressed;Thereby, it is determined that the button of a certain row and a certain column is pressed.