#include <Wire.h>

void setup() {
  Wire.begin(8);                // join i2c bus with address #8
  Serial.begin(9600);  // start serial for output
  Wire.onRequest(requestEvent); // register event
}

void loop() {
  delay(100);
}

// function that executes whenever data is requested by master
// this function is registered as an event, see setup()
void requestEvent() {
  Serial.println("received a request from I2C");
  Wire.write("hello "); // respond with message of 6 bytes
  // as expected by master
  Serial.println("Sent complete");
}