bool buttonState0;
bool buttonState1;
int grafcet_stage_0 = 1;
int grafcet_stage_1 = 0;
void setup()
{
  Serial.begin (9600); //iniciamos monitor serial a 9600 baudios
  pinMode(13, INPUT); // CHANGE TO INPUT_PULLUP IF NO EXTERNAL LOAD RESISTOR
  pinMode(12, INPUT); // CHANGE TO INPUT_PULLUP IF NO EXTERNAL LOAD RESISTOR
  pinMode(5, OUTPUT);
  pinMode(4, OUTPUT);
}

void loop()
{
  grafcet();
  outputs();
}

void grafcet()
{
  buttonState0 = digitalRead(13);
  buttonState1 = digitalRead(12);
  if (grafcet_stage_0 == HIGH && buttonState1 == LOW ) {
    grafcet_stage_0 = 0;
    grafcet_stage_1 = 1;
  }
  if (grafcet_stage_1 == HIGH && buttonState0 == LOW ) {
    grafcet_stage_0 = 1;
    grafcet_stage_1 = 0;
  }
}

void outputs()
{
  if (grafcet_stage_0 == 1 ) {
    Serial.println("Estado 0 activado ");
    digitalWrite(5, LOW);
    digitalWrite(4, LOW);
  }
  if (grafcet_stage_1 == 1 ) {
    Serial.println("Estado 1 activado ");
    digitalWrite(5, HIGH);
    digitalWrite(4, HIGH);
  }
}