Datasheet

ManualsBrandsSTMICROELECTRONICS ManualsMicrocontrollers, Microprocessors & QuartzesEmbedded microcontroller LQFP 44 (10x10) 8-Bit 24 MHz I/O number 34

Product overview STM8S207xx, STM8S208xx

16/103 Doc ID 14733 Rev 12

4.5 Clock controller

The clock controller distributes the system clock (f

MASTER)

coming from different oscillators

to the core and the peripherals. It also manages clock gating for low power modes and

ensures clock robustness.

Features

● Clock prescaler: To get the best compromise 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. The clock signal is not switched until the new clock

source is ready. The design guarantees glitch-free switching.

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

clock to the core, individual peripherals or memory.

● Master clock sources: Four different clock sources can be used to drive the master

clock:

– 1-24 MHz high-speed external crystal (HSE)

– Up to 24 MHz high-speed user-external clock (HSE user-ext)

– 16 MHz high-speed internal RC oscillator (HSI)

– 128 kHz low-speed internal RC (LSI)

● Startup clock: After reset, the microcontroller restarts by default with an internal 2

MHz clock (HSI/8). The prescaler ratio and clock source can be changed by the

application program as soon as the code execution starts.

● Clock security system (CSS): This feature can be enabled by software. If an HSE

clock failure occurs, the internal RC (16 MHz/8) is automatically selected by the CSS

and an interrupt can optionally be generated.

● Configurable main clock output (CCO): This outputs an external clock for use by the

application.

Table 3. Peripheral clock gating bit assignments in CLK_PCKENR1/2 registers

Bit

Peripheral

clock

Bit

Peripheral

clock

Bit

Peripheral

clock

Bit

Peripheral

clock

PCKEN17 TIM1 PCKEN13 UART3 PCKEN27 beCAN PCKEN23 ADC

PCKEN16 TIM3 PCKEN12 UART1 PCKEN26 Reserved PCKEN22 AWU

PCKEN15 TIM2 PCKEN11 SPI PCKEN25 Reserved PCKEN21 Reserved

PCKEN14 TIM4 PCKEN10 I

C PCKEN24 Reserved PCKEN20 Reserved