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

const int rs = 8, en = 9, d4 = 4, d5 = 5, d6 = 6, d7 = 7;
LiquidCrystal lcd(rs, en, d4, d5, d6, d7);

void setup()
{

lcd.begin(16, 2);

pinMode(LED_BUILTIN, OUTPUT);

// initialize Timer1
cli();  // disable global interrupts
TCCR1A = 0; // set entire TCCR1A register to 0
TCCR1B = 0; // same for TCCR1B

// set compare match register to desired timer count:
OCR1A = 15624;
// turn on CTC mode:
TCCR1B |= (1 << WGM12);
// Set CS10 and CS12 bits for 1024 prescaler:
TCCR1B |= (1 << CS10);
TCCR1B |= (1 << CS12);
// enable timer compare interrupt:
TIMSK1 |= (1 << OCIE1A);
// enable global interrupts:
sei();
}

void loop()
{
}

ISR(TIMER1_COMPA_vect)
{
digitalWrite(LED_BUILTIN, !digitalRead(LED_BUILTIN));
lcd.setCursor(0, 1);
// print the number of seconds since reset:
lcd.print(millis() / 1000);
}