SAM D21 Clock System Overview

The SAM D21 MCU contains a sophisticated clocking system, which is designed to give the maximum flexibility to the user application. This system allows a system designer to tune the performance and power consumption of the device in a dynamic manner, to achieve the best trade-off between the two for a particular application.


The peripherals that control the clock distribution tree of the SAM D21 are the following:

  • System Control (SYSCTRL) - This controls the clock sources, including
    • External High Frequency and 32 kHz Oscillators,
    • Internal 8 MHz and 32 kHz RC Oscillators,
    • and Internal 48 MHz Digital Frequency Locked Loop Oscillator.
  • Generic Clock Controller (GCLK) - This controls the clock distribution system.
  • Power Manager (PM) - This generates and controls the synchronous clocks in the system.

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Clock System Configuration
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DFLL48M 48 MHz Initialization Example
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