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GD32F403xx User Manual
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The CTC is clocked by the clock of IRC48M. The IRC48M can be automatically trimmed by
CTC unit.
The I2S is clocked by the clock of CK_SYS or PLL2*2 which def ined by I2SxSEL bit in
RCU_CFG1 register.
The RTC is clocked by LXTAL clock or IRC40K clock or HXTAL clock divided by 128 (defined
which select by RTCSRC bit in backup domain control register (RCU_BDCTL). After the RTC
select HXTAL clock divided by 128, the clock disappeared when the 1.2V core domain power
of f. After the RTC select IRC40K, the clock disappeared when V
DD
power off
.
After the RTC
select LXTAL, the clock disappeared when V
DD
and V
BAT
power off
.
The FWDGT is clocked by IRC40K clock, which is forced on when FWDGT started.
5.2.2.
Characteristics
◼
4 to 32 MHz High Speed crystal oscillator (HXTAL).
◼
Internal 8 MHz RC oscillator (IRC8M).
◼
Internal 48 MHz RC oscillator (IRC48M).
◼
32,768 Hz Low Speed crystal oscillator (LXTAL).
◼
Internal 40KHz RC oscillator (IRC40K).
◼
PLL clock source can be HXTAL, IRC8M o rIRC48M.
◼
HXTAL clock monitor.
5.2.3.
Function overview
High speed crystal oscillator (HXTAL)
The high speed external crystal oscillator (HXTAL), which has a frequency from 4 to 32 MHz,
produces a highly accurate clock source for use as the system clock. A crystal with a specific
f requency 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 5-3. HXTAL clock source
OSCIN
OSCOUT
C1
C2
Crystal
The HXTAL crystal oscillator can be switched on or off using the HXTALEN bit in the control
register RCU_CTL. The HXTALSTB f lag in control register RCU_CTL indicates if the high-