#include <LiquidCrystal.h>
LiquidCrystal lcd(5,4,3,2,1,0);
void setup()
{
  lcd.begin(16,2);
  lcd.print("sec");
  DDRC=0;
  DDRB=0x0f;
  PORTC= PORTC|0x03;
  TCCR2A = 2; 
  TCCR2B = 0; 
  OCR2A = 250;
  TIMSK2 = 0;
  sei();
  Serial.begin(9600);
}
int k=0; 
char txt[3];
void loop()
{
  if((PINC&0x01)==0){
    while((PINC&0x01)==0){}
      TCCR2B= 3;
      TIMSK2 = 2;
  }
  else if (Serial.available() >= 2) {
    Serial.readBytes(txt, 2);
    if (strcmp("OA", txt) == 0) {
      PORTB =  PORTB|0xFF;
      
    }
    else if (strcmp("FA", txt) == 0) {
      PORTB = 0;
      k=0; 
      TIMSK2 = 0;
    }
}
}
ISR(TIMER2_COMPA_vect){
  if(k<2000){
    k=k+1;
  }
	else{
    
    k=0;
    PORTB=~PORTB;
  }
}