Blinking LED using AVR atmega16

         Blinking a LED using 555 timer ic is simple, you can do the similar job using AVR atmega16. This is a simple program, perhaps simplest, and an introduction to Atmega16. To make a led blink you have to set (logic 1) and reset (logic 0) a pin of the controller continuously.

         there's a code for blinking a LED connected to any pin of portA of the controller.

#include<avr/io.h>

#include<util/delay.h>

int main(void)

{

DDRA=0xFF;            // set portA as out put

while(1)                     // run forever

{

PORTA=0xFF;          //All the pins of portA is set

_delay_ms(1000);      //wait  for 1sec

PORTA=0x00;          //all the pins of portA is reset

_delay_ms(1000);      // wait for 1 sec

}

return(0);

}

        DDR is data direct resister, DDR determines whether a particular pin of a port will work as an input or as an output, writing logic 1 to DDR makes the pin behave as output pin, writing logic 1 to DDR makes the pin behave as input pin. As we I wrote DDRA=0xFF, it will make all pins of portA work as output pin. Suppose you need only PA2 ( pin3 of portA ) as output pin, you need to write 1 to Bit 0 of  data direction resister for portA (DDRA). You can write like this 

                                                            DDRA=0x01; 

                                                                   or

                                                             DDRA|=(1<<PA2);

                                                                   or

                                                             DDRA|=_BV(2);   

          Blinking LED using avr timers:

The previous program seems very easy, but it has a major drawback, we are making the pins of portA on and                    

off by writing a software code, which in terns making the CPU of the controller busy all the time. Atmega16 has dedicated hardware for counting, you can set a value up to which the counter will count, after each count a flag bit will set, depending on the value of that flag bit you can set and reset a pin of PortA to toggle a LED, or simply you can run an interrupt service routine every time the flag get set. Remember you have to reset the flag bit each time.

        To make a led blink using AVR timer you need to go through this tutorial .

Code:

#include <avr/io.h>
#include <avr/interrupt.h>

int main (void)
{
   DDRB |= (1 << 0); // Set LED as output

   TCCR1B |= (1 << WGM12); // Configure timer 1 for CTC mode

   TIMSK |= (1 << OCIE1A); // Enable CTC interrupt

   sei(); //  Enable global interrupts

   OCR1A   = 15624; // Set CTC compare value to 1Hz at 1MHz AVR clock, with a prescaler of 64

   TCCR1B |= ((1 << CS10) | (1 << CS11)); // Start timer at Fcpu/64

   for (;;)
   {

   }
}

ISR(TIMER1_COMPA_vect)
{
   PORTB ^= (1 << 0); // Toggle the LED 
}

The tutorial and the following data may help you to understand the above code:

Code:

// timer 1 

   /* tccr1a & tccr1b breakdown 

   tccr1a 

    bits: 

      7      6      5      4      3     2     1     0 

    com1a1 com1a0 com1b1 com1b0 foc1a foc1b wgm11 wgm10 

      1      0      1      0      0     0     1     0 = 0xA2 

    

   tccr1b 

    bits: 

      7      6      5      4      3     2     1     0 

    icnc1 ices1     -    wgm13  wgm12 cs12  cs11  cs10 

      0      0      0      1      1     0     1     1 = 0x1B 

    

   we setup clk/64 prescale, mode 14 fast pwm, clear oc1x on compare match, set oc1x at top 

    

   wgm13 wgm12 wgm11 wgm10 

     0     0     0     0 = mode  0, normal 

     0     0     0     1 = mode  1, pwm, phase correct, 8-bit 

     0     0     1     0 = mode  2, pwm, phase correct, 9-bit 

     0     0     1     1 = mode  3, pwm, phase correct, 10-bit 

     0     1     0     0 = mode  4, ctc 

     0     1     0     1 = mode  5, fast pwm, 8-bit 

     0     1     1     0 = mode  6, fast pwm, 9-bit 

     0     1     1     1 = mode  7, fast pwm, 10-bit 

     1     0     0     0 = mode  8, pwm, phase and freq correct 

     1     0     0     1 = mode  9, pwm, phase and freq correct 

     1     0     1     0 = mode 10, pwm, phase correct 

     1     0     1     1 = mode 11, pwm, phase correct 

     1     1     0     0 = mode 12, ctc 

     1     1     0     1 = mode 13, reserved! 

     1     1     1     0 = mode 14, fast pwm 

     1     1     1     1 = mode 15, fast pwm 

    

   cs12 cs11 cs10 

     0    0    0 = no clock source, timer disabled 

     0    0    1 = clk / 1 

     0    1    0 = clk / 8 

     0    1    1 = clk / 64 

     1    0    0 = clk / 256 

     1    0    1 = clk / 1024 

     1    1    0 = external clock T1, falling edge 

     1    1    1 = external clock T1, rising edge 

    

   com1x1 com1x0 x = either a or b 

      0      0 = look at datasheet 

      0      1 = as these functions 

      1      0 = change for different 

      1      1 = timer modes 

   */