4 x 4 matrix keyboard recognition example analysis

   In the single-chip microcomputer application system, the keyboard is one of the indispensable components of human-computer dialogue. When there are relatively few keys, we can connect one key to one single-chip microcomputer I/O port, but when many keys are needed and I/O resources are relatively tight, using a matrix keyboard is undoubtedly the best choice. The
    4 x 4 matrix keyboard is the most commonly used keyboard form, and it is also a keyboard recognition technology that must be mastered when getting started with single-chip microcomputers. Below we will use an example to illustrate the recognition method of the 4 x 4 matrix keyboard. As shown in the figure below, we connect the keys in the form of a matrix, so that 16 keys can be recognized using 8 I/O ports, saving I/O port resources.

    Our recognition idea is this: when we first use it, we first let the lower four bits of the P1 port output a low level and the upper four bits output a high level, that is, let the P1 port output 0xF0. When scanning the keyboard, we read P1 port to see if P1 is still 0xF0. If it is still 0xF0, it means that no key is pressed; if it is not 0xF0, we wait for about 10ms, then read P1 port again, and confirm whether it is 0xF0 again. This is to prevent misidentification caused by jitter interference. If not, it means that a key is really pressed. We can read the key code to identify which key is pressed.
    Take the 0 key as an example. When it is initially used, P1 outputs 0xF0. When the 0 key is pressed, the state of the upper four bits should be 1110, that is, P1 is 0xE0, and then let P1 output 0x0F, and the state of the lower four bits should be 0111, that is, P1 is 0x07, and the two readings are ANDed to get 0xE7.
    Now we connect a two-common-anode digital tube to P2 port and P3 port respectively to display the key value of the key we press. P2 port is connected to data output, and P30 and P31 ports are connected to bit selection. For example, when the 0 key is pressed, 00 is displayed; when the 1 key is pressed, 01 is displayed; when the 15 key is pressed, 15 is displayed... The implemented simulation circuit and program are as follows: #include  // header file unsigned char num[]={ 0xc0,0xf9,0xa4,0xb0,0x99,  // digital tube common anode type code 0x92,0x82,0xf8,0x80,0x90 }; unsigned char Mykey=0; // save the current key value void delay_nms(unsigned int t)  // 12M crystal oscillator has a delay of about 1MS {  unsigned int i,j; for(i=t;i>0;i--)  for(j=112;j>0;j--)  ; } void GetKey(void)  // scan the key and store the key value in  Mykey { unsigned char X,Y,Z  ; P1=0xf0; if(P1!=0xf0) { delay_nms(10); P1=0xf0; if(P1!=0xf0) { X=P1; //Save the first read number  0xe0 P1=0x0f; Y=P1;  //Save the second read number   0x07 Z=X|Y;  //0xe7 P1=0xff ; while(P1!=0XFF);//Wait for the button to be released switch(Z) { case 0xe7:  Mykey=1;break; case 0xd7:  Mykey=2;break; case 0xb7:  Mykey=3;break;  case 0x77:  Mykey=4;break; case 0xeb:  Mykey=5;break; case 0xdb:  Mykey=6;break; case 0xbb:  Mykey=7;break; case 0x7b:  Mykey=8;break; case 0xed:  Mykey=9;break; case 0xdd:  Mykey=10;break; case 0xbd:  Mykey=11;break; case 0x7d:  Mykey=12;break; case 0xee:  Mykey=13;break; case 0xde:  Mykey=14;break; case 0xbe:  Mykey=15;break; case 0x7e:  Mykey=16;break; default :  Mykey=0; break; } } } } //Main function  void main() { unsigned char m,n  ; delay_nms(1); while(1)  //Continuous loop { GetKey()  ;  //Scan the keyboard m=Mykey/10;  //Get the high bit of the key value





 
               
   

  
 
 
  
  
 
 
  

 
 
 
 
  
    
   
 
 
 
 
   
 
 
    
 
  
  
   
  
  
  
  
  
  
  
  
  
  
  
  
  
   
 
 
 
 





   
    
 
    
    
  n=Mykey;    //Get the low bit of the key value
  P3=0X00;   //The digital tube is blanked
  P2=num[m]; P3=0X01; //Display the high bit of the key value
  P3=0X00;     //The digital tube is blanked
  P2=num[n]; P3=0X02;   //Display the high bit of the key value
 }
}