6.5.7.2 System Control and Clocks
System control determines the overall operation of the device. It provides information about the device, controls power-saving features, controls the clocking of the device and individual peripherals, and handles reset detection and reporting.
- Device identification information: version, part number, SRAM size, flash memory size, and so on
- Power control
- On-chip fixed low dropout (LDO) voltage regulator
- Hibernation module manages the power-up and power-down 3.3-V sequencing and control for the core digital logic and analog circuits
- Low-power options for MCU: sleep and deep-sleep modes with clock gating
- Low-power options for on-chip modules: software controls shutdown of individual peripherals and memory
- 3.3-V supply brownout detection and reporting through interrupt or reset
- Multiple clock sources for the system clock. The MCU is clocked by the system clock (SYSCLK) that is distributed to the processor and integrated peripherals after clock gating. The SYSCLK frequency is based on the frequency of the clock source and a divisor factor. A PLL is provided for the generation of system clock frequencies in excess of the reference clock provided. The reference clocks for the PLL are the PIOSC and the main crystal oscillator. The following clock sources are provided to the MCU:
- 16-MHz precision oscillator (PIOSC)
- Main oscillator (MOSC): A frequency-accurate clock source by one of two means: an external single-ended clock source is connected to the OSC0 input pin, or an external crystal is connected across the OSC0 input and OSC1 output pins.
- Low-frequency internal oscillator (LFIOSC): On-chip resource used during power-saving modes.
- Hibernate RTC oscillator (RTCOSC): A clock that can be configured to be the 32.768-kHz external oscillator source from the HIB module or the HIB low-frequency clock source (HIB LFIOSC), which is in the HIB module.
- Flexible reset sources
- Power-on reset (POR)
- Reset pin assertion
- Brownout reset (BOR) detector alerts to system power drops
- Software reset
- Watchdog timer reset
- Hibernation module event
- MOSC failure
- 128-bit unique identifier for individual device identification