Clocking

Clock Inputs

All clocks on the system are derived from one of the following clock inputs (oscillators and internal generators:)

Crystals

• XOSC1: External 12MHz oscillator
  • Provides primary system clock reference
• XOSC32K: External 32.768kHz oscillator
  • Runs in standby for RTC

FLLs

• DFLL48M: 48MHz
  • Used for USB reference clk
  • Uses external 32kHz osc for reference

PLLs

• DPLL0: 120MHz
  • CPU core clock

Clock Sources

The above clock inputs are then synthesized into multiple clock sources, each used by a different set of peripherals:

• GCLK0: 120MHz
  • Sourced from DPLL0 / 1
  • General high speed clock
• GCLK1: 48MHz 
  • Sourced from DFLL48M
  • Intended for USB use
• GCLK3: 32.768kHz
  • Sourced from XOSC32K
  • SERCOM slow clock
• GCLK4: 12MHz
  • Sourced from XOSC1
  • General low speed clock
• GCLK5: 32.768kHz
  • Sourced from ultra low power 32kHz osc

Clock Consumers

• CPU core: GCLK0
  • Clock division factor: /1
  • Low power clock: /4
  • Backup domain: /8
  • High-speed: /1