RPi. GPIO GPIO.getmode() function

Another new RPi.GPIO feature that I discovered last week is GPIO.getmode(). This appeared in RPi.GPIO 0.5.11 and allows you to query RPi.GPIO to see whether GPIO.setmode() has been set up as BCM, BOARD, or UNSET mode. This could be useful if you are running a suite of scripts or modules which work together. GPIO.getmode() returns…

-1 if GPIO.setmode() is not set
11 if GPIO.setmode(GPIO.BCM) is active
10 if GPIO.setmode(GPIO.BOARD) is active

Below you can see a live python session showing what you get when you use GPIO.getmode() with different modes set…

Why Did You Bother Setting Up An Input?

Good question. Glad you asked. Once you’ve set the mode, you can only change it once you’ve done a GPIO.cleanup(). But you can only do GPIO.cleanup() once you’ve configured a port. So you can’t flick between GPIO modes without first setting up a port, then cleaning up. Apart from testing, as I’m doing here, it’s most unlikely anyone would actually want to do that. So it’s probably a bit of a non-issue. I always use BCM numbering, so wouldn’t need to do that.

Let’s have a closer look at that live Python session to see what’s happening…

>>> from RPi import GPIO      # bring in the needed library
>>> mode = GPIO.getmode()     # read the mode into variable
>>> print mode                # print the value
-1                            # -1 is the output

>>> GPIO.setmode(GPIO.BCM)    # set BCM mode
>>> mode = GPIO.getmode()     # read the mode into variable
>>> print mode                # print the value
11                            # 11 is the output

Now we need to configure an input port because we can’t switch between modes without using cleanup(), which won’t work unless we’ve configured a port.

>>> GPIO.setup(24, GPIO.IN)   # set up an input
>>> GPIO.cleanup()            # clean up

>>> GPIO.setmode(GPIO.BOARD)  # set BOARD mode
>>> mode = GPIO.getmode()     # read the mode into variable
>>> print mode                # print the value
10                            # 10 is the output

How About A Little Script?

Let’s write a little script that we can use to show all of this in action.

from RPi import GPIO
from time import sleep
modes = {-1:"Unset", 11:"BCM", 10:"BOARD"}

mode = GPIO.getmode()
print("Your Pi is in ", modes[mode], " mode")
sleep(3)
print("Changing to BCM mode")
GPIO.setmode(GPIO.BCM)
mode = GPIO.getmode()
print("Your Pi is now in ", modes[mode], " mode")
sleep(3)

GPIO.setup(24, GPIO.IN)   # configure a port so can cleanup
GPIO.cleanup()            # cleanup so can set mode again

print("Changing to BOARD mode")
GPIO.setmode(GPIO.BOARD)
mode = GPIO.getmode()
print("Your Pi is now in ", modes[mode], " mode")
sleep(3)
print("Exiting - we're done!")

The output from this script looks like this…

It may not be something you’ll use every day – or even at all. But it’s good to know it’s there in case you need it. I include it for completeness as I like to document all the features of RPi.GPIO.

RasPiO^® GPIO Reference Aids

Our sister site RasPiO has three really useful reference products for Raspberry Pi GPIO work...

1. Portsplus port ID board
2. GPIO Ruler with RPi.GPIO code
3. GPIO Zero Ruler with GPIO Zero code