I2C addressing (7-bit and 10-bit) in Embedded C - Mini Project: Build & Apply

I2C Addressing (7-bit and 10-bit)

📖 Scenario: You are working on a small embedded system that communicates with sensors using the I2C protocol. Each sensor has an address that can be either 7-bit or 10-bit. You need to prepare the addresses correctly before sending them on the I2C bus.

🎯 Goal: Build a simple C program that stores I2C device addresses, distinguishes between 7-bit and 10-bit addresses, and prepares the addresses for communication by shifting them as required.

📋 What You'll Learn

Create an array of device addresses with both 7-bit and 10-bit values

Create a variable to hold the number of devices

Write a loop to process each address and prepare it for I2C communication

Print the original and prepared addresses for each device

💡 Why This Matters

🌍 Real World

Embedded systems often communicate with sensors and devices using I2C. Correctly preparing device addresses is essential for reliable communication.

💼 Career

Understanding I2C addressing and bit manipulation is important for embedded software engineers working with microcontrollers and hardware interfaces.

1

Create the I2C device addresses array

Create an array called device_addresses of type unsigned int with these exact values: 0x3C (7-bit), 0x1FF (10-bit), 0x50 (7-bit), and 0x2AA (10-bit).

Embedded C

# Create the device_addresses array with the given values
// Your code here

Need a hint?

Use curly braces to list the values inside the array.

2

Create a variable for the number of devices

Create an int variable called num_devices and set it to the number of elements in the device_addresses array.

Embedded C

unsigned int device_addresses[] = {0x3C, 0x1FF, 0x50, 0x2AA};
// Create num_devices to hold the number of devices
// Your code here

Need a hint?

Use sizeof to calculate the number of elements in the array.

3

Prepare addresses for I2C communication

Write a for loop using int i from 0 to num_devices - 1. Inside the loop, create an unsigned int variable called prepared_address. If the address is 7-bit (less than 128), shift it left by 1 bit. If it is 10-bit (128 or more), shift it left by 1 bit and set bit 0 to 1. Use device_addresses[i] to get the current address.

Embedded C

unsigned int device_addresses[] = {0x3C, 0x1FF, 0x50, 0x2AA};
int num_devices = sizeof(device_addresses) / sizeof(device_addresses[0]);
// Loop through device_addresses and prepare each address
// Your code here

Need a hint?

Use bitwise shift << and bitwise OR | operators.

4

Print original and prepared addresses

Inside the for loop, add a printf statement to print the original address and the prepared address in hexadecimal format. Use 0x%X format specifier. Print exactly like this: Original: 0x3C, Prepared: 0x78 for each device.

Embedded C

unsigned int device_addresses[] = {0x3C, 0x1FF, 0x50, 0x2AA};
int num_devices = sizeof(device_addresses) / sizeof(device_addresses[0]);

for (int i = 0; i < num_devices; i++) {
    unsigned int prepared_address;
    if (device_addresses[i] < 128) {
        prepared_address = device_addresses[i] << 1;
    } else {
        prepared_address = (device_addresses[i] << 1) | 1;
    }
    // Print original and prepared addresses
    // Your code here
}

Need a hint?

Use printf("Original: 0x%X, Prepared: 0x%X\n", device_addresses[i], prepared_address); inside the loop.