GD32W51x User Manual
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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 32K RC oscillator (IRC32K)
The internal RC oscillator has a frequency of about 32 kHz and is a low power clock source
for the Real Time Clock circuit or the Free Watchdog Timer. The IRC32K offers a low cost
clock source as no external components are required. The IRC32K RC oscillator can be
switched on or off by using the IRC32KEN bit in the Reset source/clock Register
(RCU_RSTSCK). The IRC32KSTB flag in the Reset source/clock Register RCU_RSTSCK
will indicate if the IRC32K clock is stable. An interrupt can be generated if the related interrupt
enable bit IRC32KSTBIE in the Clock Interrupt Register (RCU_INT) is set when the IRC32K
becomes stable.
System clock (CK_SYS) selection
After the system reset, the default CK_SYS source will be IRC16M and can be switched to
HXTAL or CK_PLLP or CK_PLLDIG by changing the System Clock Switch bits, SCS, in the
Clock configuration register 0, RCU_CFG0. When the SCS value is changed, the CK_SYS
will continue to operate using the original clock source until the target clock source is stable.
When a clock source is directly or indirectly (by PLL or PLLDIG) used as the CK_SYS, it is
not possible to stop it.
HXTAL clock monitor (CKM)
The HXTAL clock monitor function is enabled by the HXTAL Clock Monitor Enable bit,
CKMEN, in the Control Register (RCU_CTL). This function should be enabled after the
HXTAL start-up delay and disabled when the HXTAL is stopped. Once the HXTAL failure is
detected, the HXTAL will be automatically disabled. The HXTAL Clock Stuck interrupt Flag,
CKMIF, in the Clock Interrupt Register, RCU_INT, will be set and the HXTAL failure event will
be generated. This failure interrupt is connected to the Non-Maskable Interrupt, NMI, of the
Cortex-M33. If the HXTAL is selected as the clock source of CK_SYS or PLL and CK_PLLP
used as system clock, the HXTAL failure will force the CK_SYS source to IRC16M and the
PLL will be disabled automatically. If the HXTAL is selected as the clock source of any PLLs,
the HXTAL failure will force the PLL closed automatically.
Clock output capability
The clock output capability is ranging from 32kHz to 180MHz. There are several clock signals
can be selected via the CK_OUT0 clock source selection bits, CKOUT0SEL, in the Clock
Configuration Register 0 (RCU_CFG0). The corresponding GPIO pin should be configured in
the properly Alternate Function I/O (AFIO) mode to output the selected clock signal. The
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