Led blinking program in c for 8051.

A Led blinking is a basic program. In this article, we will learn how to interface led with 8051 micro-controller. The 8051 is basic micro-controller and it’s the best for a beginner. In 8051 when we have turned the power on, all I/O pins have the high value. Means that initially all I/O pins work as input except PORT 0 because in 8051 all ports have the inbuilt pull-up resistor except PORT 0.

So when we want to make the port pin as output we have to write 0 first time on that pin. In this article, we will learn, how to write a Led blinking program for 8051.

Suppose a scenario where we want to toggle a led which attached with 2nd Pin of PORT 2.

Steps to write the Program

Firstly you have to select the port pin for led.
You have to configure the pin as an output to write the first value 0.
Now pin configured as the output, if you have passed 1 or 0 on that pin it will directly reflect on it.

Here I am describing some method to write a led toggling program

Method 1

In this method, we use the sbit (single bit) keyword to select the port pin. It allows accessing of a single bit of an SFR register.

Syntax to use sbit

sbit Any_Name = Px^y;

x is port 0,1,2 or 3.
y is pin o,1,..7.

#include<reg51.h>

sbit ToggleLed = P2^1;    //pin connected to toggle Led

void Delay(const unsigned int uCount) //Function to provide delay
{
    unsigned int uLoop1=0;
    unsigned int uLoop2=0;

    for(; uLoop1 < uCount; uLoop1++)
    {
        for(uLoop2=0; uLoop2 <65535; uLoop2++)
        {}
    }
}

int main()
{
    ToggleLed=0; //configuring as output pin

    while(1)
    {
        ToggleLed=1; //Make pin high
        Delay(2);
        ToggleLed=0; // Make pin low
        Delay(2);
    }
}

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Method 2

In this method, I have created a macro IN_BINARY, which takes input in 1 and 0 format. It set and reset the PORT Pin corresponding the input binary value.

#include<reg51.h>

#define LED  P2     //Port 2 connected to  Led

#define IN_BINARY(b7,b6,b5,b4,b3,b2,b1,b0) ((b7 << 7)|(b6 << 6)|(b5 << 5)|(b4 << 4)|(b3 << 3)|(b2 << 2)|(b1 << 1)|b0)

void Delay(const unsigned int uCount) //Delay function
{
    unsigned int uLoop1=0;
    unsigned int uLoop2=0;

    for(; uLoop1 < uCount; uLoop1++)
    {
        for(uLoop2=0; uLoop2 <65535; uLoop2++)
        { }

    }
}

int main()
{
    LED=0xfd; //configuring as output port

    while(1)
    {
        LED=IN_BINARY(1,1,1,1,1,1,0,1);
        Delay(2);
        LED=IN_BINARY(1,1,1,1,1,1,1,1);
        Delay(2);
    }
}

Method 3

In this method, I am using the bit-wise operator to set and clear the bit. In below example, I have created two macro SET_BIT and CLEAR_BIT which are using to set and clear the PIN of PORT 2.

#include<reg51.h>

#define LED  P2     //Port 2 connected to  Led
#define SET_LED(x)  (1<<x)     //Macro to set the Pin
#define CLEAR_LED(x) (~(1<<x))  //Macro to clear the Pin

void Delay(const unsigned int uCount) //Delay function
{
    unsigned int uLoop1=0;
    unsigned int uLoop2=0;

    for(; uLoop1 < uCount; uLoop1++)
    {
        for(uLoop2=0; uLoop2 <65535; uLoop2++)
        { }
    }
}

int main()
{
    LED=0xfd; //configuring as output port

    while(1)
    {
        LED |= SET_LED(1);  //set the 2nd bit
        Delay(2);
        LED &= CLEAR_LED(1);  //clear the 2nd bit
        Delay(2);
    }
    return 0;
}