Electronic – arduino – I2C master’s output is always 255

arduinoarduino unocode-reviewi2cmicrocontroller

We are using two Arduino UNOs as a master/slave for this I2C protocol. We used the first Arduino (slave) as a sensor that will input dummy data (in this case, temperature data). The Arduino (master) should be able to output what the slave has input, but every time we run it, the output is always 255 instead of the temperature data.

We don't know what is wrong with the code, but we want to read the real data. Can anyone help us?

Here is the code we use for the Master:

// Include Arduino Wire library for I2C 
#include <Wire.h>

// Define Temp Slave I2C Address
#define TEMP_ADDRESS 9

void setup() {
Wire.begin(); // Initialize I2C communications as Master 

Serial.begin(9600); // Setup serial monitor 
Serial.println(">>>MASTER IS READY<<<"); 
Serial.println('\n');
}

void loop() { //Temperature 
delay(50); 

Wire.requestFrom(TEMP_ADDRESS, 12); 
Serial.print("TEMP ADDRESS: "); 
Serial.println(TEMP_ADDRESS); 
Serial.println("Receive data from TEMP Slave"); 

byte MasterReceivedTemp = Wire.read();

Serial.print("Temperature = "); 
Serial.println(MasterReceivedTemp);


Serial.println('\n');
}

Best Answer

Instead of discarding the return value from Wire.requestFrom(TEMP_ADDRESS, 12);, test the return value to determine whether or not the Wire.requestFrom worked correctly:

byte numBytesReceived = Wire.requestFrom(TEMP_ADDRESS, /* quantity */ 12); 
if (numBytesReceived == 0) {
  Serial.print("** error: device not found **");
}
else if (numBytesReceived < 12) {
  Serial.print("** error: incomplete transfer **");
}
else {
  Serial.print("++ device reply received ++");
}

Documentation is here:

https://www.arduino.cc/en/Reference/WireRequestFrom

See also this Q&A about using Arduino as an I2C slave:

https://arduino.stackexchange.com/questions/43007/why-is-a-delay1-necessary-before-wire-requestfrom

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