/*
 * I2C Echo Server
 * Receive one byte from Master, echo the same byte to Master.
 */
#define MY_ADDRESS  0x0B

#include <Wire.h>

volatile byte received;
volatile int count = 0;

void setup() {
  Serial.begin(9600);

  Wire.begin(MY_ADDRESS);
  Serial.println("--- Echo Server ---");

  Wire.onReceive(receiveCommand);
  Wire.onRequest(sendAnswer);
}

void loop() {
  static int lastCount = 0;

  if (count != lastCount) {
    Serial.print(lastCount + 1); Serial.print(" ");
    printChar(received);
    lastCount++;
  }
}

/*  
 * Receive a byte from Master  
 */
void receiveCommand(int howMany) {
  received = Wire.read();
  count++;
}

/* 
 * Send a byte to Master 
 */
void sendAnswer() {
  Wire.write(received);
}

/*
 * Utility print byte received/sent
 */
void printChar(byte car) {
  Serial.print("Char ");
  byte bit = 0x80;
  for (int i = 0; i < 8; i++) {
    byte digit = car & bit;
    Serial.print(digit ? '1' : '0');
    bit >>= 1;
  }
  Serial.println();
}