51 Microcontroller Basics Matrix Keyboard 4X4

principle:

16 keyboards can be controlled through eight pins. The upper four bits control the rows and the lower four bits control the columns.

Code:

#include

#define SMG P0 //Macro definition digital tube

#define KEY P1 //Macro definition matrix keyboard

typedef unsigned char u8;

typedef unsigned int u16;

u8 sum; //Define a global variable to save the value of the key

u8 SMG_Code[17]={0x3f,0x06,0x5b,0x4f,0x66,0x6d,0x7d,0x07,

0x7f,0x6f,0x77,0x7c,0x39,0x5e,0x79,0x71,0xff}; //The content displayed by the digital tube

void delay(u16 i)

{

while(i--);

}

void KEY_J(void) //Matrix keyboard function

{

u8 a=0; //A local variable is defined

KEY=0x0f; //When I define 0x0f, it means I start column scanning, from high to low

if(KEY!=0x0f) //KEY=0x0f was defined before. If there is a change, it should be that a button has been pressed.

{

delay(1000);//normal debounce

if(KEY!=0x0f)

{

switch(KEY)//This is interesting, because here we need to determine which column of keys is pressed. One side of the key is low level. After the connection, the high level will be pulled low, so the pin will become low level. Find the corresponding column and you will know which column it is.

{

case 0x07:sum=1;break;

case 0x0b:sum=2;break;

case 0x0d:sum=3;break;

case 0x0e:sum=4;break;

}

KEY=0xf0; //Column scanning is completed, now start row scanning

switch(KEY)//In order, the pressed pin will turn to low level to determine which row is pressed.

{

case 0x70:sum=sum;break; //The number obtained in the first row is the column

case 0xb0:sum=sum+4;break;//The number obtained in the second row is the column plus 4, and each subsequent row adds 4 to the number.

case 0xd0:sum=sum+8;break;

case 0xe0:sum=sum+12;break;

}

}

}

//It's okay not to add it, but it will be more stable if it is added.

while((a<50)&&(KEY!=0xf0)) //Detect the key release detection, which means that when you keep pressing this button, the next execution will be performed after 0.05 seconds, or the following will be executed when you release it.

{

delay(100);

a++;

}

}

void main(void)

{

while(1)

{

KEY_J(); //Call matrix keyboard function

SMG=SMG_Code[sum]; //Nigital tube display

}

}

operation result:

Click a corresponding one to display it.