GigaDevice Semiconductor GD32F10 Series, Руководство пользователя

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GD32F10x User Manual
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Figure 5-4. HXTAL clock source in bypass mode
OSCIN OSCOUT
Exte rnal cl ock
Internal 8M RC oscillators (IRC8M)
The internal 8M RC oscillator, IRC8M, has a fixed frequency of 8 MHz and is the default clock
source selection for the CPU when the device is powered up. The IRC8M oscillator provides
a lower cost type clock source as no external components are required. The IRC8M RC
oscillator can be switched on or off using the IRC8MEN bit in the control register RCU_CTL.
The IRC8MSTB flag in the control register RCU_CTL is used to indicate if the internal 8M RC
oscillator is stable. The start-up time of the IRC8M oscillator is shorter than the HXTAL crystal
oscillator. An interrupt can be generated if the related interrupt enable bit, IRC8MSTBIE, in
the Clock interrupt register, RCU_INT, is set when the IRC8M becomes stable. The IRC8M
clock can also be used as the system clock source or the PLL input clock.
The frequency accuracy of the IRC8M can be calibrated by the manufacturer, but its operating
frequency is still less accurate than HXTAL. The application requirements, environment and
cost will determine which oscillator type is selected.
If the HXTAL or PLL is the system clock source, to minimize the time required for the system
to recover from the Deep-sleep Mode, the hardware forces the IRC8M clock to be the system
clock when the system initially wakes-up.
Phase locked loop (PLL)
There is one internal Phase Locked Loop, named PLL.
The PLL can be switched on or off by using the PLLEN bit in the RCU_CTL register. The
PLLSTB flag in the RCU_CTL register will indicate if the PLL clock is stable. An interrupt can
be generated if the related interrupt enable bit, PLLSTBIE, in the RCU_INT register, is set as
the PLL becomes stable.
The PLL is closed by hardware when entering the Deepsleep/Standby mode or HXTAL
monitor fail when HXTAL used as the source clock of the PLL.
Low speed crystal oscillator (LXTAL)
The low speed external crystal or ceramic resonator oscillator, which has a frequency of
32,768 Hz, produces a low power but highly accurate clock source for the Real Time Clock
circuit. The LXTAL oscillator can be switched on or off using the LXTALEN bit in the backup