Mega (Master Writer)/ UNO (Slave Receiver) I2C Problem

Projects Programming
1

Hi all...

I have been working on the master/slave I2C communication between a MEGA (master) and an UNO (slave) microcontrollers to send a very simple character from the MEGA to the UNO that will trigger a shield on the UNO to carry out its programmed portion. For now I am simply using the example provided in the Wire.h library...

MEGA as MASTER:

//Master_writer using MEGA


#include <Wire.h>

void setup()
{
  Wire.begin(); // join i2c bus (address optional for master)
}

byte x = 0;

void loop()
{
  Wire.beginTransmission(4); // transmit to device #4
  Wire.write("x is ");        // sends five bytes
  Wire.write(x);              // sends one byte  
  Wire.endTransmission();    // stop transmitting

  x++;
  delay(500);
}

UNO as the SLAVE

//Slave_receiver using UNO


#include <Wire.h>

void setup()
{
  Wire.begin(4);                // join i2c bus with address #4
  Wire.onReceive(receiveEvent); // register event
  Serial.begin(9600);           // start serial for output
}

void loop()
{
  delay(100);
}

// function that executes whenever data is received from master
// this function is registered as an event, see setup()
void receiveEvent(int howMany)
{
  while(1 < Wire.available()) // loop through all but the last
  {
    char c = Wire.read(); // receive byte as a character
    Serial.print(c);         // print the character
  }
  int x = Wire.read();    // receive byte as an integer
  Serial.println(x);         // print the integer
}

I have a very silly question when it comes to the serial windows of each device.... Do I hit send on the MEGA then plug the UNO to the computer USB port then open its serial window to monitor the result?

I know, I know its silly but I really need to know.

Thanks.
Yesenia

2

Try it both ways, see what works. Is probably not that critical.
If one way doesn't work, use the other.

3

You never know for sure that master and slave are in sync unless you synchronize on some token.
This token can be a \n (newline) or < or ....