GD32W51x User Manual
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PLLDIG clock source can be HXTAL
PLLI2S clock source can be HXTAL
HXTAL clock monitor
6.2.3.
Function overview
High speed crystal oscillator (HXTAL)
The high speed external crystal oscillator (HXTAL), which has a frequency from 20 to 52 MHz,
produces a highly accurate clock source for use as the system clock. A crystal with a specific
frequency must be connected and located close to the two HXTAL pins. The external resistor
and capacitor components connected to the crystal are necessary for proper oscillation.
Figure 6-3. HXTAL clock source
OSCIN
OSCOUT
C1
C2
Crystal
The HXTAL crystal oscillator can be switched on or off using the HXTALEN/HXTALP
U/HXTALREADY bit in the Control Register RCU_CTL. The HXTALSTB flag in Control
Register RCU_CTL indicates if the high-speed external crystal oscillator is stable. Wh
en the HXTAL is powered up, it will not be released for use until this HXTALSTB bit
is set by the hardware. This specific delay period is known as the oscillator “Start -up
time”. As the HXTAL becomes stable, an interrupt will be generated if the related inte
rrupt enable bit HXTALSTBIE in the Interrupt Register RCU_INT is set. At this point t
he HXTAL clock can be used directly as the system clock source or the PLL input cl
ock.
Select external clock bypass mode by setting the HXTALBPS and HXTALEN bits in the
Control Register RCU_CTL. The CK_HXTAL is equal to the external clock which drives the
OSCIN pin.
Internal 16M RC oscillators (IRC16M)
The internal 16M RC oscillator, IRC16M, has a fixed frequency of 16 MHz and is the default
clock source selection for the CPU when the device is powered up. The IRC16M oscillator
provides a lower cost type clock source as no external components are required. The IRC16M
RC oscillator can be switched on or off using the IRC16MEN bit in the Control Register
RCU_CTL. The IRC16MSTB flag in the Control Register RCU_CTL is used to indicate if the
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Страница 389: ...GD32W51x User Manual 389 The FWDGT timeout can be more accurate by calibrating the IRC32K ...
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