What is the difference between BOARD and BCM for GPIO pin numbering?

  • When using the RPi.GPIO library in Python you have to call

    import RPi.GPIO as GPIO
    

    and then

    GPIO.setmode(GPIO.BOARD)
    

    or

    GPIO.setmode(GPIO.BCM)
    

    What is the difference between these two options?

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  • mirams

    mirams Correct answer

    7 years ago

    I got the information below from here.

    The GPIO.BOARD option specifies that you are referring to the pins by the number of the pin the the plug - i.e the numbers printed on the board (e.g. P1) and in the middle of the diagrams below.

    The GPIO.BCM option means that you are referring to the pins by the "Broadcom SOC channel" number, these are the numbers after "GPIO" in the green rectangles around the outside of the below diagrams:

    Unfortunately the BCM numbers changed between versions of the Pi1 Model B, and you'll need to work out which one you have guide here. So it may be safer to use the BOARD numbers if you are going to use more than one Raspberry Pi in a project.

    • The Model B+ uses the same numbering as the Model B r2.0, and adds new pins (board numbers 27-40).
    • The Raspberry Pi Zero, Pi 2B and Pi 3B use the same numbering as the B+.

    Pi1 Model B+, Pi 2B, Pi Zero and Pi 3B: GPIO pin numbering diagram


    Pi 1 Model B Revision 2.0:

    GPIO pin numbering diagram


    Pi 1 Model B Revision 1.0: GPIO pin numbering diagram

    And for completeness the A is the same as later model B boards and the A+ is the same as the B+.

    It's annoying. Just put two small numbers by each pin. Seriously @LadyAda

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Content dated before 6/26/2020 9:53 AM