（4） Independent key

Previously, I recalled the relevant contents of key output , Now you can continue to work on the contents of the key input , In this section, we will find out the relevant contents of an independent key to recall the relevant contents of key input , Make an... By the judgment of an independent key led The light is on and off .

1. About keys

The keyboard is divided into coding keyboard and non coding keyboard , The recognition of the coding keys on the keyboard is realized by a special hardware encoder , And generate code number or key value is called coding keyboard , Such as computer keyboard . The keyboard recognized by software programming is called non coding keyboard . Non coding keyboard is divided into independent keyboard and determinant keyboard . The keyboard on the single-chip microcomputer is generally a non coding keyboard , In this section, I mainly talk about the independent keyboard .

2. Hardware

In fact, the detection of cases is relatively simple , The detection principle of our button is very simple , We first pass gpio The port is connected with the key and the ground , As shown in the figure below ：

our gpio As input, it defaults to high level , At this time, we check the status of the four buttons at the same time , If gpio Low level detected , Then this button is pressed . But in practice, when we press , He didn't immediately switch from high to low , It's a period of jitter , Is a period of high and low levels , We can complete the work by hardware and software , But the hardware circuit is usually used to eliminate the jitter , This is more complicated and costly , So we basically choose the way of software anti shake , If a key has been pressed , We delayed about 10ms about , Check again , If it is still low level , It proves that the key was pressed .

3. Software

        After pressing the key, the corresponding led The main procedures for light on are as follows ：

#include "key.h"
void delay(int xms){
	int i,j;
	for(i = 0;i < xms;i++){
		for(j = 0;j < 100;j++);
	}
}
int key_scan(){ 
	if(k0==0){
		delay(10);
		if(k0==0){
			led0 = !led0;
		}
		while(!k0);
		
	}
	else if(k1==0){
		delay(10);
		if(k1==0){
			led1 = !led1;
		}
		while(!k1);
	}
	else if(k2==0){
		delay(10);
		if(k2==0){
			led2 = !led2;
		}
		while(!k2);
	} 
	if(k3==0){
		delay(10);
		if(k3==0){
			led3 = ~led3;		
		}
		while(!k3);
	}
	else {
	}
	return 0;
}	  

The principle has been made clear , By the way, put the calling function and the header file together , The header file code is as follows ：

#ifndef _KEY_H_
#define _KEY_H_
#include "reg52.h"
sbit k1 = P3^1;
sbit k0 = P3^0;
sbit k2 = P3^2;
sbit k3 = P3^3;
sbit led0 = P2^0;
sbit led1 = P2^1;
sbit led2 = P2^2;
sbit led3 = P2^3;
int key_scan();
void delay();
#endif

The main function calling functions are as follows ：

#include "reg52.h"
#include "key.h"
void main(){
	while(1){

		key_scan();
	}
}

Here we are , Our individual buttons are complete