27.6.4.2 Asynchronous Edge Detection Mode (No Debouncing)

The EXTINT edge detection operates synchronously or asynchronously, as selected by the Asynchronous Control Mode bit for external pin x in the External Interrupt Asynchronous Mode register (ASYNCH.ASYNCH[x]). The EIC edge detection is operated synchronously when the Asynchronous Control Mode bit (ASYNCH.ASYNCH[x]) is ‘0’ (default value). It is operated asynchronously when ASYNCH.ASYNCH[x] is written to ‘1’.

In Synchronous Edge Detection Mode, the external interrupt (EXTINT) or the NMI pins are sampled using the EIC clock as defined by the Clock Selection bit in the Control A register (CTRLA.CKSEL). The External Interrupt flag (INTFLAG.EXTINT[x]) or Non-Maskable Interrupt flag (NMIFLAG.NMI) is set when the last sampled state of the pin differs from the previously sampled state. The EIC clock is needed in this mode.

In Asynchronous Edge Detection Mode, the external interrupt (EXTINT) pins or the NMI pins set the External Interrupt flag or Non-Maskable Interrupt flag (INTFLAG.EXTINT[x] or NMIFLAG) directly. The EIC clock is not needed in this mode.