#include <Wire.h>

#define NODE_ADDRESS  0x42
#define PIN_LED       3

byte rcvData = 31;

void setup() {
  pinMode(PIN_LED, OUTPUT);
  
  Wire.begin(NODE_ADDRESS);
  Wire.onReceive(dataReceive);
  Wire.onRequest(dataRequest);
}

void loop() {
  analogWrite(PIN_LED, rcvData);
}

void dataReceive(int numBytes) {
  while(Wire.available()) { 
    rcvData = Wire.read();
  }
}

void dataRequest() {
  Wire.write(rcvData);
}