Master Clock Sources; Hse; Figure 21. Hse Clock Sources - ST STM8S Reference Manual

RM0016
9.1

Master clock sources

4 different clock sources can be used to drive the master clock:
●
1-24 MHz high speed external crystal oscillator (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)
Each clock source can be switched on or off independently when it is not used, to optimize
power consumption.
9.1.1

HSE

The high speed external clock signal (HSE) can be generated from two possible clock
sources:
●
HSE external crystal/ceramic resonator
●
HSE user external clock

Figure 21. HSE clock sources

The resonator and the load capacitors have to be placed as close as possible to the
oscillator pins in order to minimize output distortion and start-up stabilization time. The
loading capacitance values must be adjusted according to the selected oscillator.
Hardware configuration
(I/O available)
EXTERNAL
SOURCE
OSCIN
C
L1
LOAD
CAPACITORS
Doc ID 14587 Rev 8
Clock control (CLK)
OSCOUT
OSCOUT
C
L2
79/449