GPIO pin numbering (BCM vs BOARD) in Raspberry Pi - Quick Revision & Key Differences

Recall & Review

beginner

What does BCM stand for in Raspberry Pi GPIO pin numbering?

BCM stands for Broadcom SOC channel. It refers to the pin numbering based on the Broadcom chip's internal numbering.

beginner

What does BOARD mean in Raspberry Pi GPIO pin numbering?

BOARD refers to the physical pin numbering on the Raspberry Pi's GPIO header, counting pins from 1 to 40 based on their physical location.

intermediate

Why might you choose BCM numbering over BOARD numbering?

BCM numbering is useful because it matches the chip's internal pin names, making code more consistent across different Raspberry Pi models.

beginner

How do you set the pin numbering mode to BCM in Python using RPi.GPIO?

You use the command: GPIO.setmode(GPIO.BCM) to select BCM numbering mode.

intermediate

What could happen if you confuse BCM and BOARD numbering when wiring your Raspberry Pi?

You might connect to the wrong pins, causing your circuit to not work or even damage your Raspberry Pi or connected components.

Which GPIO pin numbering mode uses the physical pin locations on the Raspberry Pi header?

A BOARD

B BCM

C WIRINGPI

D GPIO

BOARD numbering counts pins by their physical position on the header.

What command sets the GPIO numbering mode to BCM in Python's RPi.GPIO library?

A GPIO.mode(GPIO.BCM)

B GPIO.setmode(GPIO.BOARD)

C GPIO.setup(GPIO.BCM)

D GPIO.setmode(GPIO.BCM)

GPIO.setmode(GPIO.BCM) sets the numbering to Broadcom SOC channel mode.

If you want your code to work on different Raspberry Pi models without changing pin numbers, which mode is better?

A Neither

B BOARD

C BCM

D Both are the same

BCM numbering refers to the chip pins, which stay consistent across models.

How many pins does the Raspberry Pi 40-pin header have in BOARD numbering?

A 40

B 20

C 28

D 26

The Raspberry Pi 40-pin header has 40 physical pins numbered 1 to 40.

What is a risk of mixing up BCM and BOARD numbering when connecting hardware?

A Code runs faster

B Pins may be connected incorrectly causing failure or damage

C No risk, they are interchangeable

D GPIO pins become disabled

Wrong pin connections can cause circuits to fail or damage components.

Explain the difference between BCM and BOARD GPIO pin numbering on a Raspberry Pi.

Think about chip vs physical layout.

Describe why choosing the correct GPIO pin numbering mode is important when programming Raspberry Pi hardware.

Consider what happens if you wire wrong pins.

Practice

1. Which GPIO pin numbering mode uses the physical pin numbers on the Raspberry Pi header?

easy

A. BOARD numbering mode

B. BCM numbering mode

C. WIRING numbering mode

D. PIN numbering mode

Solution

1. Step 1: Understand GPIO numbering modes

   GPIO pins can be numbered by their physical location (BOARD) or by the Broadcom chip numbering (BCM).

2. Step 2: Identify physical pin numbering

   BOARD mode refers to the physical pin numbers on the Raspberry Pi header.

3. Final Answer:

   BOARD numbering mode -> Option A

4. Quick Check:

   Physical pins = BOARD [OK]

Hint: BOARD mode matches physical pin numbers on the header [OK]

Common Mistakes:

• Confusing BCM with physical pin numbers
• Thinking BCM is the physical numbering
• Assuming WIRING or PIN modes exist

2. Which of the following is the correct way to set GPIO pin numbering to BCM mode in Python?

easy

A. GPIO.setmode(GPIO.BOARD)

B. GPIO.setupmode(GPIO.BCM)

C. GPIO.mode(GPIO.BCM)

D. GPIO.setmode(GPIO.BCM)

Solution

1. Step 1: Recall the correct function to set GPIO mode

   The function to set numbering mode is GPIO.setmode().

2. Step 2: Use the correct constant for BCM mode

   GPIO.BCM is the constant for BCM numbering mode.

3. Final Answer:

   GPIO.setmode(GPIO.BCM) -> Option D

4. Quick Check:

   Use setmode with BCM constant [OK]

Hint: Use GPIO.setmode(GPIO.BCM) to select BCM numbering [OK]

Common Mistakes:

• Using GPIO.mode instead of GPIO.setmode
• Using BOARD instead of BCM constant
• Calling GPIO.setupmode which doesn't exist

3. Given the code snippet:

import RPi.GPIO as GPIO
GPIO.setmode(GPIO.BOARD)
GPIO.setup(7, GPIO.OUT)
GPIO.output(7, GPIO.HIGH)

Which physical pin is set HIGH?

medium

A. Pin 11 on the physical header

B. GPIO pin number 7 on the Broadcom chip

C. Pin 7 on the physical header

D. GPIO pin number 11 on the Broadcom chip

Solution

1. Step 1: Identify the numbering mode used

   The code uses GPIO.setmode(GPIO.BOARD), so pin numbers refer to physical header pins.

2. Step 2: Check which pin is set HIGH

   GPIO.setup(7, GPIO.OUT) and GPIO.output(7, GPIO.HIGH) set physical pin 7 HIGH.

3. Final Answer:

   Pin 7 on the physical header -> Option C

4. Quick Check:

   BOARD mode pin 7 = physical pin 7 [OK]

Hint: BOARD mode means pin number is physical header pin [OK]

Common Mistakes:

• Confusing BOARD pin 7 with BCM GPIO 7
• Assuming pin 7 means BCM numbering
• Mixing physical pin numbers with BCM numbers

4. What is wrong with this code snippet?

import RPi.GPIO as GPIO
GPIO.setmode(GPIO.BCM)
GPIO.setup(10, GPIO.OUT)
GPIO.output(10, GPIO.HIGH)

Assuming the LED is wired to physical pin 10 on the header.

medium

A. Pin 10 in BCM does not match physical pin 10 wiring

B. GPIO.setmode(GPIO.BOARD) should be used instead

C. GPIO.output() requires pin number as string

D. GPIO.setup() cannot use BCM numbering

Solution

1. Step 1: Understand numbering mismatch

   GPIO.setmode(GPIO.BCM) means pin numbers refer to Broadcom chip pins, not physical pins.

2. Step 2: Check wiring vs numbering

   Physical pin 10 corresponds to BCM GPIO 15. The code uses BCM pin 10 (physical pin 19), so it does not control the wired physical pin 10.

3. Final Answer:

   Pin 10 in BCM does not match physical pin 10 wiring -> Option A

4. Quick Check:

   BCM 10 controls physical 19 ≠ pin 10 [OK]

Hint: Match numbering mode to wiring to avoid pin mismatch [OK]

Common Mistakes:

• Assuming physical pin numbers work with BCM mode
• Using string instead of int for pin number
• Thinking GPIO.setup can't use BCM numbering

5. You want to control an LED connected to physical pin 12 on the Raspberry Pi header. Which code snippet correctly sets the pin HIGH using BCM numbering?

hard

A. GPIO.setmode(GPIO.BOARD)
GPIO.setup(12, GPIO.OUT)
GPIO.output(12, GPIO.HIGH)

B. GPIO.setmode(GPIO.BCM)
GPIO.setup(18, GPIO.OUT)
GPIO.output(18, GPIO.HIGH)

C. GPIO.setmode(GPIO.BCM)
GPIO.setup(12, GPIO.OUT)
GPIO.output(12, GPIO.HIGH)

D. GPIO.setmode(GPIO.BOARD)
GPIO.setup(18, GPIO.OUT)
GPIO.output(18, GPIO.HIGH)

Solution

1. Step 1: Identify physical pin 12's BCM number

   Physical pin 12 corresponds to BCM GPIO 18 on Raspberry Pi.

2. Step 2: Use BCM numbering mode and correct pin

   Set mode to GPIO.BCM and use pin 18 in setup and output.

3. Final Answer:

   GPIO.setmode(GPIO.BCM) GPIO.setup(18, GPIO.OUT) GPIO.output(18, GPIO.HIGH) -> Option B

4. Quick Check:

   Physical pin 12 = BCM 18, use BCM mode [OK]

Hint: Convert physical pin to BCM before coding [OK]

Common Mistakes:

• Using physical pin number with BCM mode
• Using BCM pin number with BOARD mode
• Mixing pin numbers without conversion