Why I2C is used in Embedded C - Challenge Your Understanding

Challenge - 5 Problems

🧠 Conceptual

intermediate

Why is I2C preferred for connecting multiple sensors?

Imagine you want to connect several sensors to a microcontroller using a communication protocol. Why is I2C often chosen for this task?

A Because I2C uses wireless signals to connect devices without wires.

B Because I2C requires a separate wire for each device, making it easier to isolate signals.

C Because I2C uses only two wires to connect multiple devices, saving pins and wiring complexity.

D Because I2C can only connect two devices, making it simpler to manage.

💡 Hint

Think about how many wires are needed to connect many devices and how I2C handles addressing.

I2C uses just two wires (SDA and SCL) to connect multiple devices by assigning each a unique address. This reduces wiring complexity and saves microcontroller pins.

🧠 Conceptual

intermediate

What is a key advantage of I2C over SPI in embedded systems?

Both I2C and SPI are common communication protocols. What is a main advantage of I2C compared to SPI?

A I2C requires fewer wires and supports multiple devices on the same bus.

B I2C is faster than SPI in all cases.

C I2C uses separate chip select lines for each device.

D I2C does not require a clock signal.

💡 Hint

Consider how many wires each protocol uses and how devices are selected.

I2C uses only two wires and supports multiple devices with unique addresses, while SPI needs separate chip select lines for each device, increasing wiring complexity.

❓ Predict Output

advanced

What is the output of this I2C device scanning code snippet?

Consider this embedded C code snippet that scans for I2C devices on the bus and prints their addresses:

Embedded C

for (uint8_t addr = 1; addr < 128; addr++) {
    if (i2c_start(addr << 1 | I2C_WRITE)) {
        printf("Device found at 0x%02X\n", addr);
        i2c_stop();
    }
}

A Prints device addresses in decimal format.

B Prints all device addresses found on the I2C bus in hexadecimal format.

C Prints nothing because the loop starts at 0.

D Causes a runtime error due to invalid shift operation.

💡 Hint

Look at how the address is shifted and printed.

The code shifts the 7-bit address left by 1 and adds the write bit, then tries to start communication. If successful, it prints the address in hex.

❓ Predict Output

advanced

What error does this I2C initialization code produce?

Analyze this embedded C code snippet for I2C initialization:

Embedded C

void i2c_init() {
    TWBR = 0x48; // Set bit rate
    TWSR = 0x02; // Set prescaler bits
    TWCR = (1 << TWEN); // Enable TWI
    TWDR = 0xFF; // Load data register
}

A Runtime error due to writing to TWDR during initialization.

B No error; code initializes I2C correctly.

C Compilation error because TWBR is not declared.

D Logical error: TWDR should not be set during initialization.

💡 Hint

Consider the purpose of TWDR during initialization.

TWDR is the data register used during data transmission, not during initialization. Setting it here is a logical mistake but not a syntax error.

🧠 Conceptual

expert

Why does I2C use open-drain/open-collector lines for SDA and SCL?

In I2C communication, the data (SDA) and clock (SCL) lines are open-drain or open-collector. Why is this design used?

A To allow multiple devices to pull the line low without causing damage, enabling safe bus sharing.

B To increase the speed of data transfer by actively driving the line high and low.

C To reduce power consumption by keeping the lines always high.

D To prevent any device from pulling the line low, ensuring only the master controls the bus.

💡 Hint

Think about how multiple devices communicate on the same wire safely.

Open-drain/open-collector lines allow devices to pull the line low but never drive it high directly. A pull-up resistor brings the line high when no device pulls it low. This prevents conflicts and damage when multiple devices share the bus.