Skip to main content


Clock Inputs

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


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


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


  • 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