High-Speed Clock (Hsi/Hse) - WCH CH32V003 Series Reference Manual

CH32V003 Reference Manual

3.3.2 High-speed clock (HSI/HSE)

HSI is a high-speed clock signal generated by the system's internal 24MHz RC oscillator. HSI RC oscillator
can provide system clock without any external devices. It has a short start-up time. HSI is enabled and disabled
by setting the HSION bit in the RCC_CTLR register, and the HSIRDY bit indicates whether the HSI RC
oscillator is stable or not. The system defaults HSION and HSIRDY to 1 (it is recommended not to turn them
off). If the HSIRDYIE bit in the RCC_INTR register is set, the corresponding interrupt will be generated.
l
Factory calibration: The difference of manufacturing process will cause different RC oscillation
frequency for each chip, so HSI calibration is performed for each chip before it is shipped. After system
reset, the factory calibration value is loaded into HSICAL[7:0] of the RCC_CTLR register.
l User tuning: Based on different voltages or ambient temperatures, the application can adjust the HSI
frequency by using the HSITRIM[4:0] bits in the RCC_CTLR register.
Note: If the HSE crystal oscillator fails, the HSI clock is used as a backup clock source (clock safety system).
HSE is an external high speed clock signal, including external crystal/ceramic resonator generation or external
high speed clock feed.
l External Crystal/Ceramic Resonator (HSE Crystal): An external 4-25MHz oscillator provides a more
accurate clock source for the system. Further information can be found in the Electrical Characteristics
section of the datasheet. The HSE crystal can be turned on and off by setting the HSEON bit in the
RCC_CTLR register. The HSERDY bit indicates whether the HSE crystal oscillation is stable or not, and
the hardware feeds the clock into the system only after HSERDY position 1. If the HSERDYIE bit of the
RCC_INTR register is set, the corresponding interrupt will be generated.
Note: The load capacitor needs to be as close to the oscillator pin as possible and the capacitance value should
be selected according to the crystal manufacturer's parameters.
l External High-speed Clock Source (HSE Bypass): This mode feeds the clock source directly from the
external to the OSC_IN pin, with the OSC_OUT pin dangling. The maximum frequency supported is
25MHz. The application needs to set the HSEBYP bit to turn on the HSE bypass function with the
HSEON bit at 0, and then set the HSEON bit again.
V1.3
Figure 3-3 High-speed external crystal circuit
C
L1
Load
4～25MHz
Capacitance
C
L2
Figure 3-4 High-speed clock source circuit
External clock
f
HSE_ext
source
(Suspended)
14
OSC_IN
OSC_OUT
OSC_IN
OSC_OUT
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