Check the pull-up mode of a pin
You can use the pull() method to check the pull-up mode of a pin. The mode options are:
- Pin.PULL_UP: The pin has a default "high" value by connecting it to voltage using a resistor: "pulling up".
- Pin.PULL_DOWN: The pin has a default "low" value by connecting it to ground with a resistor: "pulling down".
The following example demonstrates how to check the pull direction of one of the pins on the XBee device and the resultant values on the pin.
- Access the MicroPython environment.
- Copy the sample code shown below.
# Import the pin module
from machine import Pin
print("\nChecking the default pull-direction of the AD0/DIO0 pin...")
pinpull = Pin.board.D0.pull()
# This call should return "1", meaning it is set to "PULL_UP".
print("AD0/DIO0 is set to: %d\n" % pinpull)
print("The two different values for pull direction can be viewed:")
print("Pin.PULL_UP: %d" % Pin.PULL_UP) # This should return "1".
print("Pin.PULL_DOWN: %d\n" % Pin.PULL_DOWN) # This should return "2".
# Now, make a pin object for pin AD0/DIO0, set as an input, and pulled
# down to ground (0).
print("Creating a pin object for AD0/DIO0, pulled DOWN...")
d0 = Pin("D0", Pin.IN, Pin.PULL_DOWN)
print("Checking the pull direction of this pin...")
pinpull = d0.pull()
print("Pull direction of AD0/DIO0: %d\n" % pinpull)
# This should return "2", since it was just set to "PULL_DOWN".
print("Checking the value present on the pin...")
pinval = d0.value()
print("Value on AD0/DIO0: %d" % pinval)
print("This should return 0, since the pin is pulled down to ground.\n")
print("Changing the pin mode to be PULL_UP.")
d0.pull(Pin.PULL_UP)
print("Checking the pull direction of this pin...")
pinpull = d0.pull()
print("Pull direction of AD0/DIO0: %d" % pinpull)
print("This should return 1, since it was just set to PULL_UP.\n")
print("Checking the value on the pin again...")
pinval = d0.value()
print("Value on AD0/DIO0: %d" % pinval)
print("This should now return 1 now, instead of 0. This means the pin was")
print("successfully \"pulled up\" to Vdd, or a logic 1.\n")
# Now that DIO0 is pulled up, we can examine how a pulled-up input works.
# Holding down the button "SW2"/"DIO0", check the value on the pin again.
print("Now we can examine how a pulled-up pin acts when connected to ground.")
_ = input("Press and hold SW2 on the XBIB board, then press Enter.")
pinval = d0.value()
print("\nValue on AD0/DIO0: %d" % pinval)
print("The value should now be 0. This is because SW2 connected the pin to")
print("ground, causing current to flow through the pull-up resistor, which")
print("dropped the voltage to 0.")-
At the MicroPython >>> prompt, type Ctrl+E to enter paste mode. The terminal displays paste mode; Ctrl-C to cancel, Ctrl-D to finish.
- At the MicroPython >>> prompt, right-click and select the Paste option.
- Once pasted, the code should execute immediately. You should see output showing the different values generated by the pull and value commands.
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