// connect 8 leds to port A its row 1 
// CONNECT 8 leds to port B its row 2 blink alternate leds  usign 0x55, 0xaa
#include <stdint.h>

#define DDRA  (*(volatile uint8_t*)0x21)
#define PORTA (*(volatile uint8_t*)0x22)

#define DDRB  (*(volatile uint8_t*)0x24)
#define PORTB (*(volatile uint8_t*)0x25)

void delay1sec(void){
    TCNT1  = 0;
    TCCR1A = 0x00;
    TCCR1B = 0x05;        // prescaler = 1024
    while (TCNT1 < 15625);
    TCCR1B = 0x00;
}

void setup() {
    DDRA = 0xFF;          // Row 1 as output
    DDRB = 0xFF;          // Row 2 as output
}

void loop() {

    // Alternate LEDs: 01010101
    PORTA = 0x55;
    PORTB = 0x55;
    delay1sec();

    // Alternate LEDs: 10101010
    PORTA = 0xAA;
    PORTB = 0xAA;
    delay1sec();
}