RM0016 Clock control (CLK)
Doc ID 14587 Rev 8 79/449
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
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.
Figure 21. HSE clock sources
Hardware configuration
External clockCrystal/ceramic resonators
OSCOUT
EXTERNAL
SOURCE
(I/O available)
OSCIN OSCOUT
LOAD
CAPACITORS
C
L2
C
L1
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