I2C acknowledge and NACK behavior in Embedded C - Mini Project: Build & Apply

I2C Acknowledge and NACK Behavior

📖 Scenario: You are working with an embedded system that communicates with a sensor using the I2C protocol. The sensor sends data bytes, and your microcontroller must acknowledge (ACK) each byte received to confirm successful reception. If the microcontroller does not want more data, it sends a Not Acknowledge (NACK) signal to stop the communication.

🎯 Goal: Build a simple C program that simulates receiving 5 bytes from an I2C sensor. Your program will send an ACK after each byte except the last one, where it will send a NACK to indicate the end of data reception.

📋 What You'll Learn

Create an array called received_bytes with exactly 5 bytes: 0x10, 0x20, 0x30, 0x40, 0x50

Create a variable called byte_count and set it to 5

Use a for loop with variable i to iterate over received_bytes

Inside the loop, print the received byte in hexadecimal format

Send an ACK after each byte except the last one, where you send a NACK

Print ACK sent or NACK sent accordingly after each byte

💡 Why This Matters

🌍 Real World

I2C communication is common in embedded systems to read sensors or communicate with other chips. Correctly sending ACK and NACK signals ensures reliable data transfer.

💼 Career

Understanding I2C acknowledge behavior is essential for embedded software engineers working with microcontrollers and hardware interfaces.

1

Create the data array for received bytes

Create an array called received_bytes with these exact 5 bytes: 0x10, 0x20, 0x30, 0x40, 0x50.

Embedded C

// Create the array received_bytes with the 5 bytes
// Your code here

Need a hint?

Use unsigned char received_bytes[5] = {0x10, 0x20, 0x30, 0x40, 0x50}; to create the array.

2

Create a variable for the number of bytes

Create an integer variable called byte_count and set it to 5.

Embedded C

unsigned char received_bytes[5] = {0x10, 0x20, 0x30, 0x40, 0x50};
// Create byte_count variable
// Your code here

Need a hint?

Use int byte_count = 5; to store the number of bytes.

3

Loop through the bytes and simulate ACK/NACK

Use a for loop with variable i from 0 to byte_count - 1 to iterate over received_bytes. Inside the loop, print the byte in hexadecimal format using printf("Received byte: 0x%02X\n", received_bytes[i]). Then, if i is less than byte_count - 1, print ACK sent. Otherwise, print NACK sent.

Embedded C

unsigned char received_bytes[5] = {0x10, 0x20, 0x30, 0x40, 0x50};
int byte_count = 5;
// Loop through received_bytes and print ACK or NACK
// Your code here

Need a hint?

Use a for loop and if condition to print ACK or NACK after each byte.

4

Print the final output

Run the program to print each received byte and the corresponding ACK or NACK message.

Embedded C

unsigned char received_bytes[5] = {0x10, 0x20, 0x30, 0x40, 0x50};
int byte_count = 5;

for (int i = 0; i < byte_count; i++) {
    printf("Received byte: 0x%02X\n", received_bytes[i]);
    if (i < byte_count - 1) {
        printf("ACK sent\n");
    } else {
        printf("NACK sent\n");
    }
}

// Run the program to see output
// Your code here

Need a hint?

Run the program and check the console output matches the expected ACK and NACK messages.