Confused SCM matrix keys

        In the process of learning SCM , Matrix keys are essential modules , Next, let Xiaobian take you into the SCM matrix button ！

One 、 Scanning of matrix keys

        The matrix key is composed of sixteen keys , When we judge the position of the matrix key , We use the state machine , Row and column scanning method is also used . Don't talk much , Now let's take a look at the composition of matrix keys ！

         In the state machine , We set four states , That is, the key is not pressed 、 Key press status 、 Press the key to pop up and turn 、 Shielding status ; The row and column scanning method we use , In fact, it is to determine the unique matrix key position according to the position of rows and columns .

Two 、 Design implementation

1. Define the global variables used ：

#define kbd_io P3
#define state_0 0	  // Whether to press 
#define state_1 1 	  // Is it jitter 
#define state_2 2	  // Judge whether it bounces 
#define kbd_maskrow 0x0f	  // Shield unwanted IO
 
unsigned int key_num=16;

2. Specific implementation functions ： 

void scankbd()
{
	static char kbd_state = 0;// Used to judge the state 
	unsigned char kbd_press;
	char row;
	switch(kbd_state){
		case state_0:  // Whether to press   
			kbd_io=0x0f; P42=0; P44=0;
			kbd_press =kbd_io;   
			if(kbd_press != kbd_maskrow)
				kbd_state = state_1;
			//break;
		case state_1:   // Is it jitter    kbd_io-P3
			kbd_press =kbd_io;
			if(kbd_press != kbd_maskrow)
			{
				if((kbd_io&0x08)==0)  row=0;                      //P30 Column 
				if((kbd_io&0x04)==0)  row=1;                      //P31 Column 
				if((kbd_io&0x02)==0)  row=2;                      //P32 Column 
				if((kbd_io&0x01)==0)  row=3;                      //P33 Column 
				kbd_io=0xf0; P42=1;P44=1; 
				if(P44==0) key_num=row;                           //p44 That's ok 
				if(P42==0) key_num=row+4;                         //p42 That's ok 
				if((kbd_io&0x20)==0) key_num=row+8;               //P35 That's ok 
				if((kbd_io&0x10)==0) key_num=row+12;              //p34 That's ok 		
				kbd_state = state_2;
			}
			else
				kbd_state = state_0;
			break;
		case state_2:   // Judge whether it bounces 
			kbd_io=0x0f; P42=0; P44=0;
			kbd_press =kbd_io;
			if(kbd_press == 0x0f)	kbd_state = state_0;
			break; 
		default:        // Shield unwanted IO
			break;
	}
}