Figure 6. Clock Sources - ST STM8S Getting Started

AN2752
The values of the load capacitors C
frequency. The user can refer to the datasheet of the crystal manufacturer to select the
capacitances. For best oscillation stability C
Typical values are in the range from below 20 pF up to 40 pF (C
parasitic capacitance of the board layout also needs to be considered and typically adds a
few pF to the component values.
Recommendations
In the PCB layout all connections have to be as short as possible. Keep any additional
signals, especially those that could interfere with the oscillator, locally separated from the
PCB area around the oscillation circuit using suitable shielding.

Figure 6. Clock sources

Hardware configuration
OSC
IN
External source
Frequency: 32 kHz ... 24 MHz
Comparator hysteresis: 0.1 * V
Caution: Without prescaler, a duty cycle of maximum 45/55% must be respected
OSC
C
L1
Frequency range: 1-24 MHz
Wake-up time: < 2 ms @ 24 MHz
Oscillation mode: Preferred fundamental
Output duty cycle: Max 55/45%
I/O's: Standard I/O pins multiplexed with OSC
Maximum crystal power: 100 µW
and C
L1
AN2752 Rev 6
STM8
OSC
OUT
(I/O available)
DD
STM8
OSC
IN OUT
Q1
C
L2
Load capacitors
and OSC
IN
Cload: 10 ... 20 pF
are heavily dependent on the crystal type and
L2
and C normally have the same value.
L1 L2
load
Clock management
OUT
: 10 to 20 pF). The
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