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Table 32 Clock Source Generating HSECLK
Name
Description
External clock source
(HSECLK bypass)
Provide clock to MCU through OSC_IN pin.
The signal can be generated by ordinary function signal transmitter (in
debugging), crystal oscillator and other signal generators; the waveform
can be square wave, sine wave or triangle wave with 50% duty cycle,
and the maximum frequency is up to 26MHz.
For hardware connection, it must be connected to OSC_IN pin, ensuring
OSC_OUT pin is suspended (in high-impedance state); for MCU
configuration, the user can select this mode by setting HSEBCFG and
HSEEN bits in RCM_CTRL (clock control register).
External crystal/ceramic
resonator
(HSECLK crystal)
The clock is provided to MCU by the resonator, and the resonator
includes crystal resonator and ceramic resonator.
The frequency range is 4-26MHz.
When needing to connect OSC_IN and OSC_OUT to the resonator, it
can be enabled and disabled by setting the HSEEN bit in clock control
register RCM_CTRL (clock control register).
HSERDYFLG bit in the clock control register RCM_CTRL (clock control
register) is used to indicate whether the high-speed external oscillator is
stable. After startup, the clock is not released until this bit is set to "1" by
hardware. If interrupt is allowed in RCM_INT (clock interrupt register),
corresponding interrupt will be generated.
LSECLK low-speed external clock signal
LSECLK clock signal is generated by LSECLK external crystal/ceramic
resonator and LSECLK external clock two kinds of clock sources.
Table 33 Clock Source Generating LSECLK
Name
Description
External clock source
(LSECLK bypass)
The clock is provided to MCU through OSC32_IN pin.
The signal can be generated by ordinary function signal transmitter
(in debugging), crystal oscillator and other signal generators; the
waveform can be square wave, sine wave or triangle wave with 50%
duty cycle, and the signal frequency needs to be 32.768kHz.
For hardware connection, it must be connected to OSC32_IN pin,
ensuring OSC32_OUT pin is suspended; for MCU configuration, the
user can select this mode by setting LSEBCFG and LSEEN bits in
RCM_BD (backup domain control register).