Hse Osc Clock; External Source (Hse Bypass); External Crystal/Ceramic Resonator (Hse Crystal); Figure 7. External Clock - ST STM32F10 Series Application Note

Clocks
2.1

HSE OSC clock

The high speed external clock signal (HSE) can be generated from two possible clock
sources:
HSE external crystal/ceramic resonator (see
HSE user external clock (see
Figure 7.
1. C and C
L1
2. The value of R
(resonator series resistance).
2.1.1

External source (HSE bypass)

In this mode, an external clock source must be provided. It can have a frequency of up to
25 MHz. The external clock signal (square, sine or triangle) with a duty cycle of about 50%,
has to drive the OSC_IN pin while the OSC_OUT pin must be left in the high impedance
state (see
2.1.2

External crystal/ceramic resonator (HSE crystal)

The 4-to-16 MHz external oscillator has the advantage of producing a very accurate rate on
the main clock. The associated hardware configuration is shown in
The resonator and the load capacitors have to be connected as close as possible to the
oscillator pins in order to minimize output distortion and startup stabilization time. The load
capacitance values must be adjusted according to the selected oscillator.
For C and C
L1
25 pF range (typ.), designed for high-frequency applications and selected to meet the
requirements of the crystal or resonator. C
crystal manufacturer typically specifies a load capacitance that is the series combination of
C and C
L1
C (10 pF can be used as a rough estimate of the combined pin and board capacitance).
L2
Refer to the electrical characteristics sections in the STM32F101xx and STM32F103xx
datasheets for more details.
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External clock
Hardware configuration
OSC_IN OSC_OUT
(Hi-Z)
External source
represent the load capacitances.
L2
depends on the crystal characteristics. Typical value is in the range of 5 to 6 R
EXT
Figure 8 and Figure 7).
it is recommended to use high-quality ceramic capacitors in the 5 pF-to-
L2
. The PCB and MCU pin capacitances must be included when sizing C
L2
Figure
Figure 7)
Figure 8.
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and C
L1 L2,
AN2586 - Application note
8)
Crystal/ceramic resonators
Hardware configuration
STM32F10xxx
OSC_IN OSC_OUT
C
L1
Figure 8.
are usually the same value. The
(1)
R
EXT
C
L2
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S
and
L1