Writing commands to I2C device in Raspberry Pi - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this I2C write command code?

Consider the following Python code snippet running on a Raspberry Pi to write a byte to an I2C device. What will be printed when this code runs successfully?

Raspberry Pi

import smbus2
bus = smbus2.SMBus(1)
address = 0x20
try:
    bus.write_byte(address, 0xFF)
    print("Write successful")
except Exception as e:
    print(f"Error: {e}")

A No output

B Error: [Errno 121] Remote I/O error

C Write failed

D Write successful

💡 Hint

The code tries to write a byte and prints a success message if no error occurs.

The code writes a byte 0xFF to the device at address 0x20. If the device is connected and responds, the write succeeds and prints 'Write successful'.

🧠 Conceptual

intermediate

Which I2C address format is correct for smbus2 write commands?

When using smbus2 on Raspberry Pi to write to an I2C device, which address format should you use?

A 8-bit address including the read/write bit, e.g., 0x40

B 7-bit address without the read/write bit, e.g., 0x20

C Decimal address only, e.g., 32

D Any address format works as smbus2 auto-corrects

💡 Hint

I2C addresses are usually 7 bits; the library handles the read/write bit.

smbus2 expects the 7-bit address without the read/write bit. The library adds the read/write bit automatically.

🔧 Debug

advanced

Why does this I2C write command raise an error?

This code snippet raises an error when trying to write a byte to an I2C device. What is the most likely cause?

Raspberry Pi

import smbus2
bus = smbus2.SMBus(1)
address = 0x20
bus.write_byte_data(address, 0x01)

A Address 0x20 is invalid for I2C devices

B Using wrong bus number; should be SMBus(0)

C Missing the data byte argument in write_byte_data call

D smbus2 does not support write_byte_data method

💡 Hint

Check the method signature for write_byte_data.

write_byte_data requires three arguments: address, command/register, and data byte. The code misses the data byte argument.

📝 Syntax

advanced

Which option correctly writes a block of bytes to an I2C device?

You want to write the bytes [0x01, 0x02, 0x03] starting at register 0x10 to an I2C device at address 0x20 using smbus2. Which code snippet is syntactically correct and will run without error?

A bus.write_i2c_block_data(0x20, 0x10, [0x01, 0x02, 0x03])

B bus.write_block(0x20, 0x10, [0x01, 0x02, 0x03])

C bus.write_i2c_block(0x20, 0x10, [0x01, 0x02, 0x03])

D bus.write_block_data(0x20, 0x10, [0x01, 0x02, 0x03])

💡 Hint

Check the exact method name in smbus2 for block writes.

The correct method is write_i2c_block_data. Other options are invalid method names and cause AttributeError.

🚀 Application

expert

What is the value of 'result' after this I2C write and read sequence?

Given the following code that writes a byte to register 0x05 and then reads a byte back from the same register, what is the value of 'result' if the device echoes the written byte?

Raspberry Pi

import smbus2
bus = smbus2.SMBus(1)
address = 0x20
bus.write_byte_data(address, 0x05, 0xAB)
result = bus.read_byte_data(address, 0x05)
print(result)

A 171

B 0

C Error: Remote I/O error

D None

💡 Hint

0xAB in decimal is 171. The device echoes the byte written.

The code writes 0xAB (decimal 171) to register 0x05 and reads it back. If the device echoes correctly, result is 171.