I2C vs SPI decision matrix in Embedded C - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to initialize an I2C communication with the correct clock speed.

Embedded C

I2C_Init([1]);

Drag options to blanks, or click blank then click option'

A100000

B500000

C1000000

D2000000

Attempts:

3 left

💡 Hint

Common Mistakes

Using SPI clock speeds instead of I2C speeds.

The standard I2C clock speed is 100 kHz, so 100000 is the correct value to initialize the I2C bus.

2fill in blank

medium

Complete the code to select the SPI mode that supports full-duplex communication.

Embedded C

SPI_SetMode([1]);

Drag options to blanks, or click blank then click option'

ASPI_MODE_0

BSPI_MODE_1

CSPI_MODE_2

DSPI_MODE_3

Attempts:

3 left

💡 Hint

Common Mistakes

Confusing SPI modes with half-duplex modes.

All SPI modes support full-duplex communication, but SPI_MODE_0 is the most commonly used and simplest mode.

3fill in blank

hard

Fix the error in the code to correctly read a byte from an I2C device.

Embedded C

uint8_t data = I2C_ReadByte([1]);

Drag options to blanks, or click blank then click option'

Agpio_pin

Bspi_channel

Cdevice_address

Dbaud_rate

Attempts:

3 left

💡 Hint

Common Mistakes

Passing SPI channel or GPIO pin instead of device address.

The I2C_ReadByte function requires the device address to read data from the correct device on the bus.

4fill in blank

hard

Fill both blanks to create a decision matrix entry for choosing SPI over I2C.

Embedded C

if (speed > [1] && devices > [2]) {
    use_spi = true;
}

Drag options to blanks, or click blank then click option'

A400000

B5

C10

D100000

Attempts:

3 left

💡 Hint

Common Mistakes

Using I2C speed values or wrong device count.

SPI is preferred when speed is greater than 400 kHz and the number of devices is more than 5.

5fill in blank

hard

Fill all three blanks to complete the function that decides between I2C and SPI based on speed, device count, and wiring complexity.

Embedded C

bool choose_spi(int speed, int devices, int wiring_complexity) {
    if (speed > [1] && devices > [2] && wiring_complexity < [3]) {
        return true;
    } else {
        return false;
    }
}

Drag options to blanks, or click blank then click option'

A400000

B3

C10

D5

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing device count and wiring complexity values.

The function returns true for SPI if speed is above 400 kHz, devices are more than 5, and wiring complexity is less than 10.

Practice

1. Which communication protocol uses only 2 wires and is suitable for connecting many devices with simple wiring?

easy

A. UART

B. SPI

C. CAN

D. I2C

Solution

1. Step 1: Recall wire count for I2C

   I2C uses 2 wires: SDA (data) and SCL (clock).

2. Step 2: Compare with SPI wiring

   SPI uses 4 wires, so it is not the protocol with only 2 wires.

3. Final Answer:

   I2C -> Option D

4. Quick Check:

   2 wires = I2C [OK]

Hint: I2C always uses 2 wires, SPI uses 4 wires [OK]

Common Mistakes:

• Confusing SPI as 2-wire protocol
• Thinking UART or CAN use 2 wires for multi-device
• Mixing up data and clock lines

2. Which of the following is the correct way to describe SPI wiring in embedded C context?

easy

A. SPI uses 3 wires: TX, RX, and CLK

B. SPI uses 2 wires: SDA and SCL

C. SPI uses 4 wires: MOSI, MISO, SCLK, and SS

D. SPI uses 1 wire for data

Solution

1. Step 1: Identify SPI signal lines

   SPI uses 4 wires: MOSI (Master Out Slave In), MISO (Master In Slave Out), SCLK (clock), and SS (slave select).

2. Step 2: Eliminate incorrect options

   Options B, C, and D do not list the correct 4 SPI wires.

3. Final Answer:

   SPI uses 4 wires: MOSI, MISO, SCLK, and SS -> Option C

4. Quick Check:

   SPI = 4 wires (MOSI, MISO, SCLK, SS) [OK]

Hint: SPI always has MOSI, MISO, SCLK, and SS wires [OK]

Common Mistakes:

• Confusing SPI with I2C wire names
• Forgetting slave select (SS) wire
• Assuming SPI uses only 2 or 3 wires

3. Given the following scenario: You need to connect 8 sensors to a microcontroller and require moderate speed communication. Which protocol is best suited?

medium

A. I2C, because it supports multiple devices with simple wiring

B. SPI, because it supports many devices easily

C. SPI, because it uses only 2 wires

D. I2C, because it is faster than SPI

Solution

1. Step 1: Analyze device count and wiring complexity

   Connecting 8 sensors means many devices; I2C supports multiple devices on 2 wires easily.

2. Step 2: Consider speed and wiring

   I2C is moderate speed but simpler wiring; SPI is faster but wiring gets complex with many devices.

3. Final Answer:

   I2C, because it supports multiple devices with simple wiring -> Option A

4. Quick Check:

   Many devices + simple wiring = I2C [OK]

Hint: Many devices + simple wiring = I2C [OK]

Common Mistakes:

• Choosing SPI for many devices ignoring wiring complexity
• Assuming SPI uses 2 wires
• Thinking I2C is faster than SPI

4. You wrote code to communicate with a sensor using SPI but the data is corrupted. Which of these is a likely cause?

medium

A. Using only 2 wires instead of 4 for SPI

B. Connecting multiple devices on I2C bus

C. Using I2C speed settings for SPI communication

D. Using pull-up resistors on SPI lines

Solution

1. Step 1: Check wiring requirements for SPI

   SPI requires 4 wires; using only 2 wires can cause data corruption.

2. Step 2: Evaluate other options

   Options A and C relate to I2C or speed mismatch, less likely cause of SPI data corruption; pull-ups on SPI lines are usually not needed.

3. Final Answer:

   Using only 2 wires instead of 4 for SPI -> Option A

4. Quick Check:

   SPI needs 4 wires, missing wires cause errors [OK]

Hint: SPI needs all 4 wires connected for reliable data [OK]

Common Mistakes:

• Using I2C settings for SPI communication
• Ignoring missing wires in SPI
• Adding pull-up resistors unnecessarily on SPI

5. You want to design a system with 3 devices requiring very fast data transfer and minimal wiring complexity. Which protocol should you choose and why?

hard

A. I2C, because it uses fewer wires and supports fast speed

B. SPI, because it supports fast data transfer with fewer devices

C. I2C, because it supports many devices even if slower

D. SPI, because it uses only 2 wires and is simple

Solution

1. Step 1: Analyze device count and speed needs

   3 devices is a small number; SPI is better for fast data transfer with fewer devices.

2. Step 2: Consider wiring complexity

   SPI uses 4 wires but with fewer devices wiring is manageable; I2C is slower though uses 2 wires.

3. Final Answer:

   SPI, because it supports fast data transfer with fewer devices -> Option B

4. Quick Check:

   Few devices + fast speed = SPI [OK]

Hint: Few devices + fast speed = SPI [OK]

Common Mistakes:

• Choosing I2C for fast speed needs
• Assuming SPI uses only 2 wires
• Ignoring device count impact on wiring