#include <Wire.h>

void setup() {
  Wire1.begin();        // join I2C bus (address optional for master)
  Serial.begin(9600);  // start serial for output
}

void loop() {
  Wire1.requestFrom(16, 6);    // request 6 bytes from slave device #8

  while (Wire1.available()) { // slave may send less than requested
    Serial.write(Wire1.read());         // print the character
  }
  Serial.println();
  delay(500);
}

#include <Wire.h>

void setup() {
  Wire1.begin(16);                // join I2C bus with address #8
  Wire1.onRequest(requestEvent); // register event
}

void loop() {
  delay(1);
}

// function that executes whenever data is requested by master
// this function is registered as an event, see setup()
void requestEvent() {
  Wire1.write("hello "); // respond with message of 6 bytes
  // as expected by master
}