SPI library usage in Arduino - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to initialize SPI communication.

Arduino

#include <SPI.h>

void setup() {
  SPI.[1]();
}

void loop() {
  // Your code here
}

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

Aopen

Bbegin

Cinit

Dstart

Attempts:

3 left

💡 Hint

Common Mistakes

Using start() or init() instead of begin().

The SPI.begin() function initializes the SPI bus and must be called before using SPI communication.

2fill in blank

medium

Complete the code to send a byte of data over SPI.

Arduino

byte data = 0x42;
SPI.[1](data);

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

Atransfer

Bsend

Cwrite

DwriteByte

Attempts:

3 left

💡 Hint

Common Mistakes

Using send() or write() which are not SPI library functions.

The SPI.transfer() function sends a byte and simultaneously receives a byte over SPI.

3fill in blank

hard

Fix the error in setting the SPI clock divider to 16.

Arduino

SPI.[1](SPI_CLOCK_DIV16);

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

AsetClockDivider

BclockDivider

CsetClock

DsetClockSpeed

Attempts:

3 left

💡 Hint

Common Mistakes

Using clockDivider() or setClock() which do not exist.

The correct function to set the SPI clock speed divider is setClockDivider().

4fill in blank

hard

Fill both blanks to set SPI data mode and bit order.

Arduino

SPI.[1](SPI_MODE0);
SPI.[2](MSBFIRST);

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

AsetDataMode

BsetBitOrder

CsetClockDivider

DbeginTransaction

Attempts:

3 left

💡 Hint

Common Mistakes

Confusing setClockDivider() with data mode or bit order functions.

setDataMode() sets the SPI mode (clock polarity and phase), and setBitOrder() sets the bit order (MSB or LSB first).

5fill in blank

hard

Fill all three blanks to start an SPI transaction with settings.

Arduino

SPI.[1](SPISettings(4000000, [2], [3]));

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

AbeginTransaction

BMSBFIRST

CSPI_MODE0

DendTransaction

Attempts:

3 left

💡 Hint

Common Mistakes

Using endTransaction() instead of beginTransaction() to start.

beginTransaction() starts an SPI transaction with specified settings: clock speed, bit order, and data mode.

Practice

1. What is the main purpose of the SPI.begin() function in Arduino's SPI library?

easy

A. To close the SPI communication

B. To initialize the SPI bus and prepare it for communication

C. To set the SPI clock speed

D. To send a byte of data over SPI

Solution

1. Step 1: Understand the role of SPI.begin()

   The SPI.begin() function sets up the SPI hardware and pins for communication.

2. Step 2: Differentiate from other SPI functions

   Functions like SPI.transfer() send data, while SPI.beginTransaction() sets speed and mode, but SPI.begin() only initializes.

3. Final Answer:

   To initialize the SPI bus and prepare it for communication -> Option B

4. Quick Check:

   SPI.begin() initializes SPI [OK]

Hint: Remember: begin() always starts or initializes [OK]

Common Mistakes:

• Confusing SPI.begin() with SPI.transfer()
• Thinking SPI.begin() sets speed or mode
• Assuming SPI.begin() closes communication

2. Which of the following is the correct syntax to send a byte of data using the SPI library in Arduino?

easy

A. SPI.send(0xFF);

B. SPI.sendByte(0xFF);

C. SPI.write(0xFF);

D. SPI.transfer(0xFF);

Solution

1. Step 1: Identify the correct SPI function for sending data

   The Arduino SPI library uses SPI.transfer() to send and receive a byte simultaneously.

2. Step 2: Check syntax correctness

   Only SPI.transfer(0xFF); matches the correct function and parameter format.

3. Final Answer:

   SPI.transfer(0xFF); -> Option D

4. Quick Check:

   SPI.transfer() sends data byte [OK]

Hint: Use transfer() to send and receive SPI bytes [OK]

Common Mistakes:

• Using non-existent functions like send() or sendByte()
• Confusing SPI.transfer() with SPI.begin()
• Using write() which is not part of SPI library

3. What will be the output of this Arduino code snippet using SPI?

SPI.begin();
byte response = SPI.transfer(0xAA);
Serial.println(response, HEX);

Assuming the SPI slave device echoes back the sent byte.

medium

A. AA

B. 55

C. 00

D. FF

Solution

1. Step 1: Understand SPI.transfer() behavior

   The SPI.transfer() sends a byte and simultaneously receives a byte from the slave device.

2. Step 2: Analyze the slave device response

   The slave echoes back the sent byte 0xAA, so response will be 0xAA.

3. Final Answer:

   AA -> Option A

4. Quick Check:

   Sent byte echoed back = AA [OK]

Hint: SPI.transfer() returns the received byte immediately [OK]

Common Mistakes:

• Assuming transfer() only sends without receiving
• Expecting a different response byte
• Confusing HEX output with decimal

4. Identify the error in this Arduino SPI code snippet:

SPI.beginTransaction(SPISettings(4000000, MSBFIRST, SPI_MODE0));
SPI.transfer(0x01);
SPI.endTransaction();
SPI.begin();

medium

A. SPI.begin() should be called before SPI.beginTransaction()

B. SPI.endTransaction() is missing

C. SPI.transfer() cannot be used inside a transaction

D. SPISettings parameters are incorrect

Solution

1. Step 1: Check SPI initialization order

   SPI.begin() must be called once before starting any transaction to initialize SPI hardware.

2. Step 2: Verify transaction usage

   The code calls SPI.beginTransaction() before SPI.begin(), which is incorrect and causes errors.

3. Final Answer:

   SPI.begin() should be called before SPI.beginTransaction() -> Option A

4. Quick Check:

   Initialize SPI first with begin() [OK]

Hint: Always call SPI.begin() before transactions [OK]

Common Mistakes:

• Calling beginTransaction() before begin()
• Forgetting to call endTransaction()
• Misunderstanding SPISettings parameters

5. You want to communicate with two SPI devices on the same Arduino. How should you manage SPI transactions to avoid conflicts?

hard

A. Use SPI.transfer() without transactions for both devices

B. Call SPI.begin() twice, once for each device

C. Call SPI.beginTransaction() with each device's settings before communication and SPI.endTransaction() after

D. Connect both devices to the same chip select pin

Solution

1. Step 1: Understand SPI multi-device communication

   Each SPI device may require different speed or mode settings, so transactions help manage these safely.

2. Step 2: Use transactions properly

   Call SPI.beginTransaction() with the device's settings before communicating, then SPI.endTransaction() after to avoid conflicts.

3. Final Answer:

   Call SPI.beginTransaction() with each device's settings before communication and SPI.endTransaction() after -> Option C

4. Quick Check:

   Use transactions per device to avoid conflicts [OK]

Hint: Use beginTransaction/endTransaction per device [OK]

Common Mistakes:

• Calling SPI.begin() multiple times
• Sharing chip select pins for different devices
• Skipping transactions causing wrong settings