Getting Started with C51 MCU - Buttons

Key jitter

There is a sound when a key is pressed. Although some key press sounds are very slight, these are all vibrations caused by the collision of metal conductors; this phenomenon is called: key jitter.

If the jitter of the keys is not dealt with, the keys will cause unexpected interference to the system circuit or program. Therefore, we need to "de-bounce" the keys.

The key is effective after being pressed and lifted

Using the delay function, the key1 is pressed and then released to control the LED to flash;

#include

sbit key1 = P1^4; //key1 on the experimental board

sbit LED0 = P0^0;

unsigned char key1_down;

void delay(unsigned int delay_time)

{ 

   unsigned int j = 0;

   for(;delay_time > 0;delay_time --)

   { 

  for(j = 0;j < 125;j ++); 

   }

}

void key_pressed(void) //key scan function

{

    if(key1 == 1); //If the key is pressed

{

delay(20); //eliminate keyboard jitter

if(key1 == 1) //If the key is pressed

key1_down = 1; //Memory key1 pressed state

}

if((key1 == 0) && (key1_down == 1)) //key1 was pressed before and is now lifted

{

LED0 = !LED0; //LED flashes

key1_down = 0; //The button pressed status is cleared

}

}

void main(void) 

{

    P0 = 0x00; // Turn off all LEDs driven by P0

  while(1)

key_pressed(); //Call function    

}

The button is effective when pressed

It takes effect when the confirmation button is really pressed

/* Software debounce */                                                                                                                                  

if (0 == K1) //If a key is pressed                                                                                                                  

{                                                                                                                                             

    delay_ms(8); //delay for a while to debounce                                                                                                    

    if (0 == K1) //If a key is pressed, it is detected to be in a stable closed state                                                                                       

    {                                                                                                                               

        //Statement block; //What needs to be done after pressing the button                                                                                

    }                                                                                                                              

    while (!K1); // Release detection, if you hold down the button, the loop will continue                                                                                      

}