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AN3147

Clock management

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Clock management

3.1

STM8L101xx clock system overview

The 16 MHz high speed internal RC oscillator (HSI) is the only clock source that can be

used to drive the system clock.

The 38 kHz low speed internal RC oscillator (LSI) is only used to supply the auto-wakeup

unit (AWU) and watchdog.

Each peripheral clock can be switched on or off independently, in order to optimize power

consumption when the peripheral is not used. This is done by using the peripheral clock

gating (PCG) feature. See the “Clock control” section of the STM8L101xx reference manual

(RM0013) for more details.

3.2

STM8L05xxx, STM8L15xxx, STM8L16xxx, STM8AL31xx and

STM8AL3Lxx clock system overview

Several different clock sources can be used to drive the system clock, depending on the

product and package you use:



1-16 MHz high speed external clock from the crystal oscillator (HSE crystal)



Up to 16 MHz high speed external clock provided by the user (HSE bypass)



16 MHz high speed internal RC oscillator (HSI)



32.768 kHz low speed external crystal oscillator (LSE)



38 kHz low speed internal RC oscillator (LSI)

Each clock source can be switched on or off, depending on the actual needs of the

application. Each peripheral clock can be switched on or off independently, in order to

optimize power consumption when it is not used. This is done by using the peripheral clock

gating (PCG) feature. See the ‘Clock control’ section in the STM8L05xx, STM8L15xx,

STM8L162x, STM8AL31xx and STM8AL3Lxx microcontroller family reference manual

(RM0031) for more details.

Several clock sources can be enabled in one time. The following table shows the main

features of each clock source. STM8L and STM8AL devices offer a complete range of clock

sources to meet customer application requirements in terms of cost, accuracy and

consumption.