GigaDevice Semiconductor GD32F3x0 - Page 75

GD32F3x0 User Manual
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as ADC clock. The IRC28M RC oscillator can be switched on or off using the IRC28MEN bit
in the control register 1 (RCU_CTL1). The IRC28MSTB flag in the control register 1
(RCU_CTL1) is used to indicate if the internal 28M RC oscillator is stable. An interrupt can
be generated if the related interrupt enable bit, IRC28MSTBIE, in the interrupt register,
RCU_INT, is set when the IRC28M becomes stable.
Internal 48 MHz RC Oscillator (IRC48M)
The Internal 48 MHz RC Oscillator, IRC48M, has a fixed frequency of 48 MHz and dedicated
as USB clock or PLL source. The IRC48M RC oscillator can be switched on or off using the
IRC48MEN bit in the RCU_ADDCTL Register. The IRC48MSTB flag in the RCU_ADDCTL
register is used to indicate if the internal 48M RC oscillator is stable. An interrupt can be
generated if the related interrupt enable bit, IRC48MSTBIE in the RCU_ADDCTL register is
set when the IRC48M becomes stable.
The frequency accuracy of the IRC48M can be calibrated by the manufacturer, but its
operating frequency is still not enough accurate because the USB need the frequency must
between 48MHz with 500ppm accuracy. A hardware automatically dynamic trim performed
in CTC unit adjust the IRC48M to the needed frequency.
Low Speed Crystal Oscillator (LXTAL)
The low speed crystal or ceramic resonator oscillator, which has a frequency of 32.768 kHz,
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
generated if the related interrupt enable bit, LXTALSTBIE, in the Interrupt register RCU_INT
is set when the LXTAL becomes stable.
Select external clock bypass mode by setting the LXTALBPS and LXTALEN bits in the
backup domain control register(RCU_BDCTL). The CK_LXTAL is equal to the external clock
which drives the OSC32IN pin.
Internal 40 KHz RC Oscillator (IRC40K)
The Internal 40KHz RC Oscillator has a frequency of about 40 kHz and is a low power clock
source for the real time clock circuit or the free watchdog timer. The IRC40K offers a low cost
clock source as no external components are required. The IRC40K RC oscillator can be
switched on or off by using the IRC40KEN bit in the reset source/clock register,
RCU_RSTSCK. The IRC40KSTB flag in the reset source/clock register RCU_RSTSCK will
indicate if the IRC40K clock is stable. An interrupt can be generated if the related interrupt
enable bit IRC40KSTBIE in the Interrupt register RCU_INT is set when the IRC40K becomes
stable.