Declaring Digital Signal

I have a 3D printer (Mendel) with Generation 6 electronics board. Here is the main code for that:

[forums.reprap.org]

I have connected an Arduino to the Gen 6 board and started communication via I2C using this routine. This code goes into the Arduino:
(replace " " with <>

#include "Wire.h"

//i2c address of the gen 6
int REP_RAP_ADDR = 4;
//my address
int CP_ADDR = 5;

void receiveEvent(int howMany)
{
  while(0 < Wire.available()) // loop through all
  {
    char c = Wire.receive(); // receive byte as a character
    Serial.print(c);         // print the character       
  }
}

void sendGCode(char* GCode)
{
  Wire.beginTransmission(REP_RAP_ADDR);
  Wire.send(GCode);
  Wire.endTransmission();   
}

void setup()
{
  Wire.begin(CP_ADDR);
  Wire.onReceive(receiveEvent); // register event so that anything received on i2c is sent to the serial

  //Test gcode, this should send the machine's X, Y and Z to home
  sendGCode("G28 X0 Y0 Z0\n");
}

void loop()
{
  
}

I2C has already been initialized in the main code.
Now I need a digital signal at say pin 2 of Arduino. I have connected a LED at pin 2 and I want that LED to light up when the printer is printing and off when it is not printing. How to achieve this ??
I am guessing I need to include something in the main code as well as to the code that I have posted for Arduino, but I am not sure what or how

Edited 1 time(s). Last edit at 08/12/2011 11:18AM by Javaid Butt.