Determining I2C Address without Datasheet

Question

When setting up I2C communications, I know that it is certainly ideal to have the devices' datasheet(s), and find the I2C address of the device(s) that way. However, in some reverse-engineering applications, you don't have a datasheet available. (Or, you may just not be able to find it...)

Without the datasheet, how do you determine the default I2C address of a device? Also, what tool(s)/equipment do you need? (e.g. is a microcontroller with I2C support enough, or do you need an oscilloscope?)

Answer 1

It's fairly easy to write an I2C "ping" utility for a microcontroller. All you need to do is scan through the ~128 addresses and for each one:

1. Send I2C Start condition
2. Send a single byte representing the address, and get the ACK/NAK
3. Send the stop condition.

If there is an ACK (the data line held low on the 9th clock cycle) then a device with that address is present on the I2C bus. If there is no ACK then no device is present.

Don't forget that I2C addresses are in the upper 7 bits of the byte (the last bit is for read/write). Also, don't forget to ignore the special I2C addresses in your scan: http://www.i2c-bus.org/addressing/

As for hardware almost anything will work. Even if your device doesn't have I2C support it's a simple enough (and slow enough) protocol where you can bit bang it. Just make sure that whatever you use never drives the I2C lines high, only low (as per spec).

Answer 2

If you don't want to do it manually:

• Hook up a Raspberry Pi
• Run sudo i2cdetect -y 0
• If Run sudo i2cdetect -y 0 does not work, Run sudo i2cdetect -y 1

Answer 3

Here's a snippet of Arduino code that I use:

for (int address=1; address <= 126; address++) {
  Wire.beginTransmission(address); // Select address
  if (!Wire.endTransmission()) Serial.printf("Found device at: %02Xh\n", address); 
}

Answer 4

You can connect SCL/SDA to an Arduino board, power the I2C device up then run on the Arduino board this code:

// i2c_scanner
 //
 // This program (or code that looks like it)
 // can be found in many places.
 // For example on the Arduino.cc forum.
 // The original author is not know.
 //
 // This sketch tests the standard 7-bit addresses
 // from 0 to 127. Devices with higher bit address
 // might not be seen properly.
 //
 // Adapted to be as simple as possible by Arduino.cc user Krodal

#include <Wire.h>

void setup()
{
    Wire.begin();
    Serial.begin(115200);
    Serial.println("\nI2C Scanner");
}

void loop()
{
    byte error, address;
    int nDevices;

    Serial.println("Scanning...");

    nDevices = 0;
    for(address = 0; address <= 127; address++ )
    {
        Wire.beginTransmission(address);
        error = Wire.endTransmission();
        if (error == 0)
        {
            Serial.print("I2C device found at address 0x");
            if (address<16)
                Serial.print("0");
            Serial.print(address, HEX);
            Serial.println(" !");
            nDevices++;
        }
        else if (error==4)
        {
            Serial.print("Unknow error at address 0x");
            if (address<16)
                Serial.print("0");
            Serial.println(address,HEX);
        }
    }
    if (nDevices == 0)
        Serial.println("No I2C devices found\n");
    else
        Serial.println("done\n");
    delay(30000);
 }