class ExtInt – configure I/O pins to interrupt on external events

There are a total of 22 interrupt lines. 16 of these can come from GPIO pins and the remaining 6 are from internal sources.

For lines 0 through 15, a given line can map to the corresponding line from an arbitrary port. So line 0 can map to Px0 where x is A, B, C, … and line 1 can map to Px1 where x is A, B, C, …

def callback(line):
    print("line =", line)

Note: ExtInt will automatically configure the gpio line as an input.

extint = pyb.ExtInt(pin, pyb.ExtInt.IRQ_FALLING, pyb.Pin.PULL_UP, callback)

Now every time a falling edge is seen on the X1 pin, the callback will be called. Caution: mechanical pushbuttons have “bounce” and pushing or releasing a switch will often generate multiple edges. See: for a detailed explanation, along with various techniques for debouncing.

Trying to register 2 callbacks onto the same pin will throw an exception.

If pin is passed as an integer, then it is assumed to map to one of the internal interrupt sources, and must be in the range 16 through 22.

All other pin objects go through the pin mapper to come up with one of the gpio pins.

extint = pyb.ExtInt(pin, mode, pull, callback)

Valid modes are pyb.ExtInt.IRQ_RISING, pyb.ExtInt.IRQ_FALLING, pyb.ExtInt.IRQ_RISING_FALLING, pyb.ExtInt.EVT_RISING, pyb.ExtInt.EVT_FALLING, and pyb.ExtInt.EVT_RISING_FALLING.

Only the IRQ_xxx modes have been tested. The EVT_xxx modes have something to do with sleep mode and the WFE instruction.

Valid pull values are pyb.Pin.PULL_UP, pyb.Pin.PULL_DOWN, pyb.Pin.PULL_NONE.

There is also a C API, so that drivers which require EXTI interrupt lines can also use this code. See extint.h for the available functions and usrsw.h for an example of using this.


class pyb.ExtInt(pin, mode, pull, callback)

Create an ExtInt object:

  • pin is the pin on which to enable the interrupt (can be a pin object or any valid pin name).
  • mode can be one of: - ExtInt.IRQ_RISING - trigger on a rising edge; - ExtInt.IRQ_FALLING - trigger on a falling edge; - ExtInt.IRQ_RISING_FALLING - trigger on a rising or falling edge.
  • pull can be one of: - pyb.Pin.PULL_NONE - no pull up or down resistors; - pyb.Pin.PULL_UP - enable the pull-up resistor; - pyb.Pin.PULL_DOWN - enable the pull-down resistor.
  • callback is the function to call when the interrupt triggers. The callback function must accept exactly 1 argument, which is the line that triggered the interrupt.

Class methods

classmethod ExtInt.regs()

Dump the values of the EXTI registers.



Disable the interrupt associated with the ExtInt object. This could be useful for debouncing.


Enable a disabled interrupt.


Return the line number that the pin is mapped to.


Trigger the callback from software.



interrupt on a falling edge


interrupt on a rising edge


interrupt on a rising or falling edge