51 Single Chip Microcomputer (Twenty-five) - Independent button control LED

In the previous article about 51 MCU, we mainly talked about the application of the output function of MCU IO port, such as LED control, digital tube control, etc. In this article, we will explain how to use the MCU IO port to read the state of the key and control the LED according to the state of the key. For the introduction of the key input function of 51 MCU, please refer to the article "51 MCU (Twenty-four) - Working Principle of Independent Key"

In this article, the code of the example is shown below.

#define KEY P2 //Define key input port

#define LED P0 //Define LED output port

/************************************************************************/

/* Main function */

/************************************************************************/

void main (void)

{

KEY=0xff; //Set the key input port level to high

for(;;) //main loop

{

LED=KEY;

}

}

The code is very simple. The main code is only one line LED=KEY in the for loop. The purpose of this line of code is to assign the value of KEY to the LED. From the macro definition of the program, we can know that KEY is P2, which is the register of the 8 IO ports connected to the independent button. LED is P0, which is the register of the 8 IO ports connected to the LED. When an independent button is pressed, the level state of the IO port corresponding to P2 is pulled down, and the input is 0. When the button is released, the input is 1. In the for loop, the value of P2 is assigned to P0. When the button is pressed, the output of the IO port that controls the LED is 0, and the corresponding LED lights up. When the button is released, the output of the IO port that controls the LED is 1, and the corresponding LED goes out. Since the assignment code is in the for loop, the state of the LED will be updated in real time.