10.4.2.2.4 External Clock

The output clock of a Generator (GCLK_GENn) can be sent to an I/O pin (GCLK_IO[n]).

If the Output Enable bit in the Generator Control register (GENCTRL[n].OE) is ‘1’ and the Generator is enabled (GENCTRL[n].GENEN = ‘1’), the Generator requests its clock source and the GCLK_GENn clock is output to an I/O pin.
Note: The I/O pin must be configured as a GCLK_GENn output by writing to the corresponding PORT registers before enabling the clock output on GLKC_IO[n]. See the PORT chapter for more information.

If GENCTRL[n].OE is ‘0’, the corresponding I/O pin is set to a value selected by the Output Off Value bit field of the GENCTRL[n] register (GENCTRL[n].OOV). If GENCTRL[n].OOV is '0', the output clock will be low. If this bit is ‘1’, the output clock will be high.

If the device enters Standby sleep mode while GENCTRL[n].OE is ‘1’, the clock output on the I/O pin depends on the Run In Standby bit in the GENCTRL[n] register (GENCTRL[n].RUNSTDBY):
  • If GENCTRL[n].RUNSTDBY is ‘0’, the GCLK_IO[n] pin is held at the OOV value
  • If GENCTRL[n].RUNSTDBY is ‘1’, the GCLK_IO[n] pin outputs the GCLK_GENn clock