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;
}

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