ESP32 Forum

Posted: **Fri Sep 27, 2024 1:36 pm**

I programmed an ESP32 as an I2C slave. I was using arduino IDE to program the ESP32 and the version installed in the boards manager is 3.0.4. When I tested it with a master, the data order was incorrect on the received data. To test it at a very basic level, I wrote a piece of code where whatever the master wrote to the slave, the slave would return the double of it on the next data request. The issue is that the data is getting shifted. I receive my expected value on the second request and the first one returns the previous value (Check the master and slave outputs to understand better)

Following is the code for I2C slave

Code: Select all

#include <Wire.h>

int receivedValue = 0;
int responseValue = 0;

void setup() {
  Wire.begin(0x08); // join I2C bus with address 0x08
  Wire.onReceive(receiveEvent); // register event for receiving data from master
  Wire.onRequest(requestEvent); // register event for responding to master requests
  
  Serial.begin(115200);
}

void loop() {
  }

// This function is triggered when data is received from the master
void receiveEvent(int howMany) {
  if (Wire.available()) {
    receivedValue = Wire.read(); // Receive the number sent by the master
    responseValue = receivedValue * 2; // Double the value
    Serial.print("Received from master: ");
    Serial.print(receivedValue);
    Serial.print(", Prepared to send: ");
    Serial.println(responseValue);
  }
}

// This function is triggered when the master requests data
void requestEvent() {
  Wire.write(responseValue); // Send the doubled value back to the master
}

Following is the code for I2C master

Code: Select all

#include <Wire.h>

const int slaveAddress = 0x08; // I2C address of the slave

void setup() {
  Wire.begin(); // join I2C bus as master
  Serial.begin(115200);
}

void loop() {
  // Send numbers 1, 2, 3, 4, 5 in series
  for (int valueToSend = 1; valueToSend <= 5; valueToSend++) {
    sendAndReceive(valueToSend); // Send and receive for each number
    delay(1000);                 // 1-second delay between transmissions
  }
}

void sendAndReceive(int valueToSend) {
  // Send the value to the slave
  Wire.beginTransmission(slaveAddress);
  Wire.write(valueToSend); // Send the number to be doubled
  Wire.endTransmission();

  delay(5000); // Small delay to ensure the slave processes the request
  
  // Request 1 byte back from the slave
  Wire.requestFrom(slaveAddress, 1);
  
  if (Wire.available()) {
    int receivedValue = Wire.read(); // Read the response from the slave
    Serial.print("Sent: ");
    Serial.print(valueToSend);
    Serial.print(", Received: ");
    Serial.println(receivedValue); // Expecting the doubled value
  } else {
    Serial.println("No response from slave");
  }
}

Following is the serial output on the slave

Code: Select all

Received from master: 1, Prepared to send: 2
Received from master: 2, Prepared to send: 4
Received from master: 3, Prepared to send: 6
Received from master: 4, Prepared to send: 8
Received from master: 5, Prepared to send: 10
Received from master: 1, Prepared to send: 2
Received from master: 2, Prepared to send: 4
Received from master: 3, Prepared to send: 6
Received from master: 4, Prepared to send: 8
Received from master: 5, Prepared to send: 10

Following is the serial output from the master

Code: Select all

Sent: 1, Received: 10
Sent: 2, Received: 2
Sent: 3, Received: 4
Sent: 4, Received: 6
Sent: 5, Received: 8
Sent: 1, Received: 10
Sent: 2, Received: 2
Sent: 3, Received: 4
Sent: 4, Received: 6
Sent: 5, Received: 8

I suspect the issue is with the I2C slave. I uploaded this same slave code to an Arduino mega while the master was the same ESP32 and the response was correct without changing the data order.

ESP32 Forum

Data order getting changed in I2C in ESP32 Arduino

Data order getting changed in I2C in ESP32 Arduino