GD32W51x User Manual
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internal 16M RC oscillator is stable. The start-up time of the IRC16M oscillator is shorter than
the HXTAL crystal oscillator. An interrupt can be generated if the related interrupt enable bit,
IRC16MSTBIE, in the Clock Interrupt Register, RCU_INT, is set when the IRC16M becomes
stable. The IRC16M clock can also be used as the system clock source or the PLL input clock.
The frequency accuracy of the IRC16M 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 IRC16M clock to be the system
clock when the system initially wakes-up.
If USART0
、
USRAT2 and I2C0 select IRC16M as function clock
,
the IRC16M will be force
on according to USART0
、
USRAT2 and I2C0 function.
Phase locked loop (PLL)
There are three internal Phase Locked Loop, the PLL, PLLI2S and PLLDIG The PLLP and
PLLDIG could be used to generator system clock (no more than 180MHz) and their division-
clock which used to USBFS/TRNG/SDIO/I2S/HPDF. The PLLI2S is used to generator the
clock to I2S/HPDF.
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 PLLI2S can be switched on or off by using the PLLI2SEN bit in the RCU_CTL Register.
The PLLI2SSTB flag in the RCU_CTL Register will indicate if the PLLI2S clock is stable. An
interrupt can be generated if the related interrupt enable bit, PLLI2SSTBIE, in the RCU_INT
Register, is set as the PLLI2S becomes stable.
The PLLDIG can be switched on or off by using the PLLDIGEN/PLLDIGPU bit in the
RCU_CTL Register. The PLLDIGSTB flag in the RCU_CTL Register will indicate if the
PLLDIG clock is stable. An interrupt can be generated if the related interrupt enable bit,
PLLDIGSTBIE, in the RCU_INT Register, is set as the PLLDIG becomes stable.
The three PLLs are closed by hardware when entering the Deepsleep/Standby mode or
HXTAL monitor fail when HXTAL used as the source clock of the PLLs.
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
Domain Control Register (RCU_BDCTL). The LXTALSTB flag in the Backup Domain Control
Register (RCU_BDCTL) will indicate if the LXTAL clock is stable. An interrupt can be