18.5.3 Clocks

The OSCCTRL gathers controls for all device oscillators and provides clock sources to the Generic Clock Controller (GCLK). The available clock sources are: XOSCn, DFLL48M, and FDPLL200Mn.

The DFLL48M requires a reference clock (GCLK_DFLL48M_REF) from the GCLK. The control logic uses the oscillator output, which is also asynchronous to the user interface clock (CLK_OSCCTRL_APB). Due to this asynchronicity, writes to certain registers will require synchronization between the clock domains. Refer to Synchronization for further details.

The FDPLL200Mn require a reference clock (GCLK_DPLL) for the FDPLL output. When the optional lock timer timeout function is used, a 32KHz reference clock (GCLK_DPLL_32K) is also required. Both reference clocks can either stem from the GCLK and/or from external oscillators.