#include <SoftwareSerial.h>
#include <avr/io.h>
#define f_CPU 20000000

#define TX PA5
#define RX PA4

SoftwareSerial mySerial(RX, TX);

void setup()
{
  mySerial.begin(9600);
 DDRB=0b0000;       //switch is input in PB2. give all PB pins as input.
 DDRA=0b11111111;   //LED is output in PA7. giving all PA pins as output.
 PORTB|=(1<<2);     //pull-up PB2 internally
}
void loop()
{
  if (!(PINB&(1<<2)))      //if PB2 is 0, this condition is fulfilled
  {
  mySerial.print('0'); 
  delay(500);
  mySerial.print('1');//switch on LED in PA7
  }
 //return 0;
}