#include <SPI.h>
#include <Wire.h>

//address depend on state of A2 A1 A0
//A2 A1 A0 = 0 0 0 (Binary) → Address = 0x20
//A2 A1 A0 = 1 1 1 (Binary) → Address = 0x27
#define MCP23017 0x20

void setup() {
  Wire.begin();
  Wire.beginTransmission(MCP23017);
  // address of the IODIRA register, which control port A
  Wire.write(0x00);
  // sets all pins of port A as outputs by writing a value of 0x00 to the IODIRA register.
  Wire.write(0x00);
  Wire.endTransmission();
  delay(500);

  Wire.begin();
  Wire.beginTransmission(MCP23017);
  // address of the IODIRA register, which control port B
  Wire.write(0x01);
  // sets all pins of port B as outputs by writing a value of 0x00 to the IODIRA register.
  Wire.write(0x00);
  Wire.endTransmission();
  delay(500);
}

bool state = true;
unsigned long last_Millis = 0;

void loop() {

  if(millis() - last_Millis >= 1000){
    last_Millis = millis();
      if(state == true) {
      Wire.beginTransmission(MCP23017);
      Wire.write(0x12); // GPIOA 0x12 LED8
      Wire.write(0x00);
      Wire.endTransmission();
      
      Wire.beginTransmission(MCP23017);
      Wire.write(0x13); // GPIOB 0x13 LED9
      Wire.write(0xFF);
      Wire.endTransmission();
    }
    else {
      Wire.beginTransmission(MCP23017);
      Wire.write(0x12);
      Wire.write(0xFF);
      Wire.endTransmission();

      Wire.beginTransmission(MCP23017);
      Wire.write(0x13);
      Wire.write(0x00);
      Wire.endTransmission();
    }
    state = !state;
  }
  
}