Wire (I2C)


Registers a function to be called when a slave device receives a transmission from a master.

Parameters: handler: the function to be called when the slave receives data; this should take a single int parameter (the number of bytes read from the master) and return nothing, e.g.: void myHandler(int numBytes)

Note: This handler will lock up the device if System calls such as Particle.publish() are made within, due to interrupts being disabled for atomic operations during this handler. Do not overload this handler with extra function calls other than what is immediately required to receive I2C data. Post process outside of this handler.


// Slave Reader running on Device No.2 (Use with corresponding Master Writer running on Device No.1)

// 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

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() {