MCU 4*4 matrix keyboard

 Use the microcontroller P1 port to expand into a 4*4 keyboard. Press the key to light up the LED of the P0 port. 

The expansion of the matrix keyboard is not complicated, but the detection code part is complicated. 

IO expansion principle

    A matrix keyboard, also known as a row-column keyboard, is a keyboard that uses four I/O lines as row lines and four I/O lines as column lines.

A key is set at each intersection of a row line and a column line, so that the number of keys on the keyboard is 4*4.

This matrix keyboard structure can effectively improve the utilization rate of I/O ports in the single-chip computer system.

Detection principle

    When no key is closed, the row line and column line are open. When a key is closed, the two I/O port lines connected to the closed key are short-circuited.

    How to determine whether a key is pressed:

1. Coarse scan. The row line outputs low level, and the column line outputs high level. Read the Px port, if the data is not equal to 0x0F, a key is pressed.

2. Fine scan. The row lines output low level row by row, and other IO ports output high level. Read the Px port, if the data is not equal to the output value, a key is pressed. And the number of rows can be determined. Similarly, the column lines output low level row by row, and the number of columns can be detected.

3. Convert key codes according to row and column numbers 

code show as below:

#include 
#define uchar unsigned char  

#define LED_ON(X) P0 = ~(1<<(X)) //LED turns on at low level

uchar KeyScan(void);

void main(void)
{
	uchar key;

	while(1){
		key = KeyScan();

		if(key > 0)
		{
			key = key -1;
			LED_ON(key); 
		} 
	}
}

uchar KeyScan(void)						
{

	uchar i,val,row,col,key;

	P1 = 0xF0; //Row line set to 0, column line set to 1

	if( P1 != 0x0F0 ) //button pressed
	{
		for(i=0;i<4;i++) //row scan	
		{
			val = 0xFF&(~(1<