#include <Wire.h>

int LEDA = 0; // PA4
int receivedValue = 1;

void setup() {
  pinMode(LEDA, OUTPUT);
  Serial.begin(9600);
  Wire.begin(9); // secondary ID #9
  //Wire.begin(10); // secondary ID #10
  Wire.onReceive(dataReceive);
}

void loop() {
  Serial.println(receivedValue);
}

void dataReceive(int num) {
  if (Wire.available()) {
    receivedValue = Wire.read();
    if (receivedValue == 1) {
      digitalWrite(LEDA, HIGH);
    } else if (receivedValue == 0) {
      digitalWrite(LEDA, LOW);
    }
  }
}