GPIO pin numbering (BCM vs BOARD) in Raspberry Pi - Practice Questions

Challenge - 5 Problems

❓ Predict Output

intermediate

Understanding BCM vs BOARD numbering output

What will be the output of this Python code snippet using the RPi.GPIO library?

import RPi.GPIO as GPIO
GPIO.setmode(GPIO.BCM)
print(GPIO.getmode())

Assume the code runs without errors.

Raspberry Pi

import RPi.GPIO as GPIO
GPIO.setmode(GPIO.BCM)
print(GPIO.getmode())

A GPIO.BOARD

B 10

C GPIO.BCM

D 11

💡 Hint

Check the RPi.GPIO documentation for mode constants.

GPIO.BCM mode is represented internally by the integer 11 in RPi.GPIO. So, GPIO.getmode() returns 11 after setting BCM mode.

🧠 Conceptual

intermediate

Difference between BCM and BOARD numbering

Which statement correctly describes the difference between BCM and BOARD pin numbering on a Raspberry Pi?

A Both BCM and BOARD numbering refer to the same pin numbers but in different order.

B BOARD numbering refers to the physical pin numbers on the header, BCM refers to Broadcom chip pin numbers.

C BCM numbering refers to the physical pin numbers on the header, BOARD refers to Broadcom chip pin numbers.

D BCM numbering is deprecated and replaced by BOARD numbering.

💡 Hint

Think about what 'BOARD' and 'BCM' stand for.

BOARD numbering uses the physical pin numbers on the Raspberry Pi header. BCM numbering uses the Broadcom chip's GPIO pin numbers.

🔧 Debug

advanced

Pin numbering mode mismatch error

What error will this code produce?

import RPi.GPIO as GPIO
GPIO.setmode(GPIO.BOARD)
GPIO.setup(17, GPIO.OUT)
GPIO.output(17, GPIO.HIGH)

A No error, pin 17 is set high

B RuntimeError: The channel has not been set up as an output

C RuntimeError: GPIO pin numbering mode mismatch

D ValueError: Invalid GPIO pin number

💡 Hint

Check if pin 17 is valid in BOARD mode.

In BOARD mode, pin numbers refer to physical pins 1-40 on the header. Pin 17 is valid (maps to BCM GPIO0). The code runs without error and sets the pin high.

❓ Predict Output

advanced

Output of pin number mapping

What will this code print?

import RPi.GPIO as GPIO
GPIO.setmode(GPIO.BCM)
print(GPIO.gpio_function(18))

A 1

B 2

C 0

D 3

💡 Hint

Check what gpio_function returns for an unconfigured pin.

GPIO.gpio_function(pin) returns 0 if the pin is set as input (default). Since pin 18 is not configured, it returns 0.

🧠 Conceptual

expert

Choosing pin numbering mode for cross-platform code

You want to write a Python script using RPi.GPIO that works on different Raspberry Pi models without changing pin numbers. Which pin numbering mode should you use?

A Use BOARD mode because physical pins are consistent across models.

B Use BCM mode because GPIO numbers are consistent across models.

C Use BOARD mode because GPIO numbers are consistent across models.

D Use BCM mode because physical pins are consistent across models.

💡 Hint

Think about physical pin layout consistency.

BOARD mode uses physical pin numbers which remain consistent across Raspberry Pi models with the 40-pin header.