TWI Master

// Written by Nick Gammon
// Date: 18th February 2011
// Modified by Synthetic Physical Computing
// Date: 1st Febuary 2014

#include <Wire.h>

const int SLAVE_ADDRESS = 0x42;

// various commands we might send
enum {
    CMD_ID = 1,
    CMD_READ_A0  = 2,
    CMD_READ_A1  = 3,
    CMD_READ_A2  = 4,
    CMD_READ_A3  = 5,
    CMD_READ_D2  = 6,
    CMD_READ_D3  = 7,
    CMD_READ_D4  = 8,
    CMD_READ_D5  = 9,
    };

void sendCommand (const byte cmd, const int responseSize)
  {
  Wire.beginTransmission (SLAVE_ADDRESS);
  Wire.write (cmd);
  Wire.endTransmission ();

  Wire.requestFrom (SLAVE_ADDRESS, responseSize);
  }  // end of sendCommand

void setup ()
  {
  Wire.begin ();
  //TWBR = 12;
  Serial.begin (9600);  // start serial for output

  sendCommand (CMD_ID, 1);

  if (Wire.available ())
    {
    Serial.print ("Slave is ID: ");
    Serial.println (Wire.read (), HEX);
    }
  else
    Serial.println ("No response to ID request");

  }  // end of setup

void loop()
  {
  int val;

  sendCommand (CMD_READ_A0, 2);
  val = Wire.read ();
  val <<= 8;
  val |= Wire.read ();
  Serial.print ("Value of A0: ");
  Serial.println (val, DEC);

  sendCommand (CMD_READ_A1, 2);
  val = Wire.read ();
  val <<= 8;
  val |= Wire.read ();
  Serial.print ("Value of A1: ");
  Serial.println (val, DEC);

  sendCommand (CMD_READ_A2, 2);
  val = Wire.read ();
  val <<= 8;
  val |= Wire.read ();
  Serial.print ("Value of A2: ");
  Serial.println (val, DEC);

  sendCommand (CMD_READ_A3, 2);
  val = Wire.read ();
  val <<= 8;
  val |= Wire.read ();
  Serial.print ("Value of A3: ");
  Serial.println (val, DEC);

  sendCommand (CMD_READ_D2, 1);
  val = Wire.read ();
  Serial.print ("Value of D2: ");
  Serial.println (val, DEC);

  sendCommand (CMD_READ_D3, 1);
  val = Wire.read ();
  Serial.print ("Value of D3: ");
  Serial.println (val, DEC);

  sendCommand (CMD_READ_D4, 1);
  val = Wire.read ();
  Serial.print ("Value of D4: ");
  Serial.println (val, DEC);

  sendCommand (CMD_READ_D5, 1);
  val = Wire.read ();
  Serial.print ("Value of D5: ");
  Serial.println (val, DEC);

  delay (500);
  }  // end of loop