I2C onReceive-handler called only once

Question

I'm having trouble communicating between Arduino's over I2C. For some reason, the onReceive handler is only called once.

Master Code (sender):

#include <Wire.h>                                                                     
#include "i2csettings.h" // defines address

void setup()
{
    Wire.begin(I2C_MASTER_ADDRESS);
}

void loop()
{                   
    Wire.beginTransmission(I2C_SLAVE_ADDRESS); 
    Wire.write(0x11);
    Wire.endTransmission();

    delay(1000);       
}

Slave Code (receiver):

#include <Wire.h>
#include "i2csettings.h"

void takeAction(int);

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

    Wire.begin(I2C_SLAVE_ADDRESS);
    Wire.onReceive(takeAction);
}

void loop()
{} 

void takeAction(int nBytes)
{
    Serial.println("Action!");
}

The idea in this test-setup is to have the sender send a byte every second, and let the receiver act on this by printing a message. However, the message is only printed once. When I reset the Slave, it's printed again, but just once.

Any ideas where this may come from?

score 7 · Accepted Answer · answered Apr 05 '15 at 18:03

7

You have to make sure you read all the bytes from the stream. Other wise it seems to block. Make your event handler look like this. So you can call it multiple times.

void takeAction(int nBytes)
{
  Serial.println("Action!");
  while(Wire.available())
  {
    Wire.read();
  }
  return;
}

answered Apr 05 '15 at 18:03

theUser

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Thanks! Very good to know, even though the project has come to an end a while back. I will keep this in mind for future reference and will accept the answer when I get the chance to confirm this. – JorenHeit Apr 06 '15 at 18:18
Did you have a chance to confirm yet ? – theUser Mar 31 '18 at 15:09
Joren, my bro. Did you confirm that dude ? – theUser Feb 18 '19 at 00:42
Joren, long time bro. We should do something special for the 5 year anniversary of not choosing this as the correct answer. – theUser Jan 27 '20 at 14:45
Much appreciated :D – theUser May 20 '20 at 00:16

I2C onReceive-handler called only once

1 Answers1