STM32G474PBY3TR datasheet(29/236 Pages) STMICROELECTRONICS

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DS12288 Rev 5

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STM32G474xB STM32G474xC STM32G474xE

Functional overview

3.13

Clocks and startup

The clock controller distributes the clocks coming from different oscillators to the core and

the peripherals. It also manages clock gating for low-power modes and ensures clock

robustness. It features:

•

Clock prescaler: to get the best trade-off between speed and current consumption,

the clock frequency to the CPU and peripherals can be adjusted by a programmable

prescaler

•

Safe clock switching: clock sources can be changed safely on the fly in run mode

through a configuration register.

•

Clock management: to reduce power consumption, the clock controller can stop the

clock to the core, individual peripherals or memory.

•

System clock source: three different sources can deliver SYSCLK system clock:

–

4 - 48 MHz high-speed oscillator with external crystal or ceramic resonator (HSE).

It can supply clock to system PLL. The HSE can also be configured in bypass

mode for an external clock.

–

16 MHz high-speed internal RC oscillator (HSI16), trimmable by software. It can

supply clock to system PLL.

–

System PLL with maximum output frequency of 170 MHz. It can be fed with HSE

or HSI16 clocks.

•

RC48 with clock recovery system (HSI48): internal HSIRC48 MHz clock source can

be used to drive the USB or the RNG peripherals.

•

Auxiliary clock source: two ultra-low-power clock sources for the real-time clock

(RTC):

–

32.768 kHz low-speed oscillator with external crystal (LSE), supporting four drive

capability modes. The LSE can also be configured in bypass mode for using an

external clock.

–

32 kHz low-speed internal RC oscillator (LSI) with ±5% accuracy, also used to

clock an independent watchdog.

•

Peripheral clock sources: several peripherals (I2S, USART, I2C, LPTimer, ADC, SAI,

RNG) have their own clock independent of the system clock.

•

Clock security system (CSS): in the event of HSE clock failure, the system clock is

automatically switched to HSI16 and, if enabled, a software interrupt is generated. LSE

clock failure can also be detected and generate an interrupt.

•

Clock-out capability:

–

MCO: microcontroller clock output: it outputs one of the internal clocks for external

use by the application

–

LSCO: low speed clock output: it outputs LSI or LSE in all low-power modes.

Several prescalers allow to configure the AHB frequency, the High-speed APB (APB2) and

the low speed APB (APB1) domains. The maximum frequency of the AHB and the APB

domains is 170 MHz.

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