51 MCU key detection and signal function simulation

In the single-chip microcomputer, there is a problem of identifying buttons. The commonly used independent button circuit is as follows: 

Since mechanical contact switches are flexible and will vibrate, they need to be debounced. There are two ways to debounce: hardware debounce and software debounce. 

Hardware debounce circuit: 

Software debouncing often uses delayed debouncing: when a key is pressed, when a low level is detected, there is a delay of a period of time, usually 5 to 10ms, and then the port is detected again. If it is still a low level, it means that the key is detected to be pressed, and the same applies when the key is released.

There are generally two methods for detecting independent buttons: interrupt detection and query detection. 

The button is connected to the P3^2 pin to detect the number of times the button is pressed and released.

1. Query detection: You can directly loop the detection in the main program, or you can use a timer to detect once every 20ms. The following is a direct detection in the loop.

Main function:

#include

#include

#define uint unsigned int 

sbit in0 = P3^2; //input signal pin

uint Press_flag = 1; //button pressed flag

uint count = 0 ; //Number of key presses

void delay_ms(uint ms)

{

    uint i , j ;

    for(i = 0 ; i < ms ; i++)

    {

        for(j = 0 ; j < 333 ; j++)

        {

            _nop_() ;

        }

    }

}

void key()

{

       if(in0 == 0) //0 is detected

        {

            delay_ms(10); // Delay debounce

            if(in0 == 0) // detect 0 again

            {

                Press_flag = 0; //Indicates that the button is pressed

            }

        }

        if(Press_flag == 0) //If the key is pressed, detect if the key pops up

        {

            if(in0 == 1)

            {

                delay_ms(10) ;

                if(in0 == 1)

                {

                    count++; //Indicates the number of times the key is pressed and released

                    Press_flag = 1; // reset button pressed flag

                }

            }

        }

}

void main(void)

{ 

    while(1)

    {

          key() ;

    }

}

Signal function:

signal void test(unsigned int cc) 

{

    unsigned int i , j ;

    for(i = 0 ; i < cc ; i++)

    {

        for(j = 0 ; j < 2 ; j++)

        {

            port3 &= ~(1<<2) ;

            swatch(0.002) ;

            port3 |= 1<<2 ;

            swatch(0.002);

        }

        port3 &= ~(1<<2) ;

        swatch(0.002) ;

        swatch(0.01) ;

        for(j = 0 ; j < 2 ; j++)

        {

            port3 |= 1<<2 ;

            swatch(0.002) ;

            port3 &= ~(1<<2) ;

            swatch(0.002) ;

        }   

        port3 |= 1<<2 ;

        swatch(0.02) ;

        swatch(0.1) ;

    }

    _break_ = 1 ;

}

Signal function waveform: 

You can see that the value of count is 4 

2. Interruption detection

Main program:

#include

#include

#define uint unsigned int 

sbit in0 = P3^2 ;

uint count = 0 ;    

uint press_flag = 1 ;

void delay_ms(uint ms)

{

    uint i , j ;

    for(i = 0 ; i < ms ; i++)

    {

        for(j = 0 ; j < 333 ; j++)

        {

            _nop_() ;

        }

    }

}

void Init_INT(void)

{

    EA = 1; // Enable general interrupt

    EX0 = 1; //Open external interrupt 0

    IT0 = 1; // Falling edge triggers interrupt

}

void Int0 (void) interrupt 0

{

    EX0 = 0; //Disable external interrupt 0 to prevent frequent interrupt triggering

    delay_ms(10) ;

    if(in0 == 0)

    {

        press_flag = 0 ; //button pressed flag

    }

    if(press_flag == 0 && in0 == 1) // detect button pop-up

    {

        delay_ms(10) ;

        if(in0 == 1)

        {

            count++ ;

            press_flag = 1 ;

        }

    }

    EX0 = 1; // Enable external interrupt

}

void main(void)

{

    Init_INT(); //Interrupt initialization

    while(1)

    {

    }

}