Power Domains

SAM L21 has five digital power domains, indicated in Figure 1. This allows for power saving by limiting or powering off logic areas in the device. Most of the power domains can switch between three states:

Active state: Peripherals in the power domain are powered and ready to be used or configured.
Retention state: Main voltage supply is powered off while maintaining a low-power supply to hold the state of the registers and SRAM.
Off state: Peripherals in the domain are not powered and registers must be reprogrammed for a peripheral to be used.

Turning power domains off or to retention state allows the device to consume less power in STANDBY than what is achievable by only disabling clocks. Power domains are automatically switched between active and retention state but can also be forced to active state. The dynamical switching is known as Power Domain Gating. Power domain configurations are set in the Standby Configuration (STDBYCFG) register in the Power Manager (PM) module.