Playing with LED

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In this post we'll make a scrolling pattern on the LED's (watch the video).

Just like last time, we'll consider that we have 8 LED's connected to PortC.

Now, the LED have to be turned ON, only one at a time, and they should remain ON for some time (say, 500 milliseconds).

#include<avr/io.h>

#include<util/delay.h>   // header file for generating delay

void main()

{ DDRC=0b11111111;    // Since, PortC is output, thus, all 8 bits are declared 1

  PORTC=0x00;             // initially all LED will be off. 

/*

Note: If on your development board, the LED are connected in Active Low configuration, they will turn ON when a '0' is given. If the LED are active high, they will turn ON when '1' is given. If you are not sure whether your LED are active high or active low, just give 1 and see what happens.

Here, I am assuming that LED are active high.

*/

  while(1)   // infinite loop so that the process inside is executed all the time.

 {  

   PORTC=0b00000001;

   _delay_ms(500);

   PORTC=0b00000010;

   _delay_ms(500);

   PORTC=0b00000100;

   _delay_ms(500);

   PORTC=0b00001000;

   _delay_ms(500);

   PORTC=0b00010000;

   _delay_ms(500);

   PORTC=0b00100000;

   _delay_ms(500);

    PORTC=0b01000000;

   _delay_ms(500);

    PORTC=0b10000000;

   _delay_ms(500);

 }

}

In the above program, we make only one LED on at a time, give a delay, and then turn on the next LED and switch off the other LED by writing 1 to the LED which we want to turn ON and the rest are 0.

The above program, though simple, is cumbersome to write.

We'll write the above program in a different way utilizing the vast potential of C.

#include<avr/io.h>

#include<util/delay.h>

volatile unsigned char x=0;  

void main() 

{

DDRC=0b11111111;   // Declare entire PortC as output

PORTC=0b00000000;   // Make PortC initially 0.

while(1)

{ x=0;

  while(x<8)               // execute this part till x is less than 8

  { PORTC=(1<<x);    // shift 1 by 'x' spaces.

    _delay_ms(500);

x=x+1;           // increment x.

  }

}

} 

We would like to point out one very important thing about Embedded C at this point. 
Notice the 'volatile unsigned char x=0' before the main() ?
In embedded C, all variables that are to be used should be defined and initialized before the main() starts.