GPIO pin numbering (BCM vs BOARD) in Raspberry Pi - Visual Side-by-Side Comparison

Concept Flow - GPIO pin numbering (BCM vs BOARD)

Start: Choose Pin Numbering Mode

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BOARD Mode Selected?

Yes→Use Physical Pin Numbers

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Access Pins by Position

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Perform GPIO Actions

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BCM Mode Selected?

Yes→Use Broadcom GPIO Numbers

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Access Pins by GPIO Number

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Perform GPIO Actions

Choose between BOARD (physical pin positions) or BCM (Broadcom chip numbers) to access Raspberry Pi GPIO pins before performing actions.

Execution Sample

Raspberry Pi

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

This code sets the pin numbering to BOARD mode, sets physical pin 7 as output, and turns it on.

Execution Table

Step	Action	Pin Numbering Mode	Pin Referenced	Effect
1	Import GPIO library	None	None	GPIO module ready
2	Set mode to BOARD	BOARD	None	Pins referenced by physical position
3	Setup pin 7 as output	BOARD	Physical pin 7	Pin 7 ready for output
4	Set pin 7 HIGH	BOARD	Physical pin 7	Pin 7 output set to HIGH (on)
5	End	BOARD	Physical pin 7	Program finished

💡 Program ends after setting pin 7 HIGH in BOARD mode

Variable Tracker

Variable	Start	After Step 2	After Step 3	After Step 4	Final
Pin Numbering Mode	None	BOARD	BOARD	BOARD	BOARD
Pin 7 State	Undefined	Undefined	Configured as Output	HIGH	HIGH

Key Moments - 2 Insights

Why does setting GPIO.setmode(GPIO.BOARD) change how pins are referenced?

Because BOARD mode uses the physical pin numbers on the Raspberry Pi header, not the Broadcom chip numbers. See execution_table step 2 where mode changes to BOARD.

What happens if you use BCM numbering but reference a physical pin number?

The wrong pin will be accessed or an error may occur because BCM mode expects GPIO numbers, not physical positions. This is shown by contrasting step 2 and 3 in the execution_table.

Visual Quiz - 3 Questions

Look at the execution_table, what is the pin numbering mode after step 3?

A None

B BCM

C BOARD

D Undefined

💡 Hint

Check the 'Pin Numbering Mode' column at step 3 in the execution_table.

At which step is pin 7 configured as an output?

A Step 3

B Step 4

C Step 2

D Step 1

💡 Hint

Look at the 'Effect' column in execution_table for when pin 7 is set as output.

If you change GPIO.setmode(GPIO.BCM) in the code, what changes in the execution_table?

A Pin numbering mode stays BOARD but pin referenced changes

B Pin numbering mode changes to BCM and pin referenced changes to GPIO number

C No change in pin numbering mode or pin referenced

D Program will not run

💡 Hint

Refer to the concept_flow and execution_table showing mode selection effect on pin referencing.

Concept Snapshot

GPIO Pin Numbering Modes:
- BOARD: Use physical pin numbers on header
- BCM: Use Broadcom GPIO chip numbers
Set mode with GPIO.setmode(GPIO.BOARD) or GPIO.setmode(GPIO.BCM)
Pin references depend on chosen mode
Always set mode before accessing pins

Full Transcript

This visual execution shows how Raspberry Pi GPIO pin numbering works. First, you choose a mode: BOARD or BCM. BOARD mode uses the physical pin positions on the Pi's header, while BCM mode uses the Broadcom chip's GPIO numbers. The example code sets BOARD mode, then sets physical pin 7 as output and turns it on. The execution table traces each step, showing the mode and pin referenced. Variable tracking shows how the mode and pin state change. Key moments clarify why mode matters and what happens if you mix numbering systems. The quiz tests understanding of mode and pin setup. Remember to always set the pin numbering mode before controlling pins to avoid mistakes.