I2C vs SPI decision matrix in Embedded C - Practice Questions

Challenge - 5 Problems

❓ Predict Output

intermediate

I2C vs SPI: Which bus speed is faster?

Consider the following code snippets initializing I2C and SPI buses with typical speeds. What is the output when comparing their speeds?

Embedded C

#include <stdio.h>

int main() {
    int i2c_speed = 400000; // 400 kHz
    int spi_speed = 10000000; // 10 MHz

    if (spi_speed > i2c_speed) {
        printf("SPI is faster\n");
    } else {
        printf("I2C is faster\n");
    }
    return 0;
}

A SPI is faster

B I2C is faster

C Both have the same speed

D Compilation error

💡 Hint

Compare the numeric values of spi_speed and i2c_speed.

SPI typically runs at higher clock speeds than I2C. Here, 10 MHz (SPI) is greater than 400 kHz (I2C), so SPI is faster.

🧠 Conceptual

intermediate

I2C vs SPI: Number of wires used

Which option correctly states the number of wires used by I2C and SPI respectively?

A I2C uses 3 wires; SPI uses 3 wires

B I2C uses 2 wires; SPI uses 4 or more wires

C I2C uses 4 wires; SPI uses 2 wires

D I2C uses 1 wire; SPI uses 2 wires

💡 Hint

Recall that I2C uses SDA and SCL lines.

I2C uses two wires: SDA (data) and SCL (clock). SPI uses at least four wires: MOSI, MISO, SCLK, and SS (slave select).

❓ Predict Output

advanced

SPI data transfer behavior

What is the output of this SPI data transfer simulation code?

Embedded C

#include <stdio.h>

int main() {
    unsigned char master_tx = 0xA5; // Master sends 0xA5
    unsigned char slave_tx = 0x3C;  // Slave sends 0x3C
    unsigned char master_rx = slave_tx; // Master receives slave data
    unsigned char slave_rx = master_tx; // Slave receives master data

    printf("Master received: 0x%X\n", master_rx);
    printf("Slave received: 0x%X\n", slave_rx);
    return 0;
}

A

Master received: 0xA5
Slave received: 0x3C

B Compilation error

C

Master received: 0x00
Slave received: 0x00

D

Master received: 0x3C
Slave received: 0xA5

💡 Hint

SPI is full-duplex: master and slave exchange data simultaneously.

In SPI, the master sends data to the slave while simultaneously receiving data from the slave. Here, master receives 0x3C from slave, and slave receives 0xA5 from master.

🧠 Conceptual

advanced

I2C addressing modes

Which statement correctly describes I2C addressing modes?

A I2C supports 7-bit and 10-bit addressing modes

B I2C supports only 8-bit addressing mode

C I2C supports 4-bit and 8-bit addressing modes

D I2C supports only 16-bit addressing mode

💡 Hint

Think about how many bits are used to identify devices on the bus.

I2C devices can be addressed using either 7-bit or extended 10-bit addresses, allowing more devices on the bus.

🚀 Application

expert

Choosing between I2C and SPI for a sensor array

You have a sensor array with 8 identical sensors that need to send data to a microcontroller. The sensors require moderate speed and minimal wiring complexity. Which bus would be the best choice and why?

A SPI, because it supports longer cable lengths and fewer devices

B SPI, because it uses fewer wires and supports multiple devices without addressing

C I2C, because it uses only two wires and supports multiple devices with unique addresses

D I2C, because it requires a separate chip select line for each device

💡 Hint

Consider wiring complexity and device addressing for multiple sensors.

I2C uses only two wires regardless of the number of devices and supports addressing each sensor uniquely, making it ideal for multiple sensors with minimal wiring.