GD32VF103 User Manual
65
prescaler is not 1).
The USBFS is clocked by the clock of CK_PLL as the clock source of 48MHz.
The I2S is clocked by the clock of CK_SYS or PLL2*2 which defined 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 off. 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.
The FMC is clocked by IRC8M clock, which is forced on when IRC8M started.
5.2.2.
Characteristics
3 to 25 MHz High Speed crystal oscillator (HXTAL) .
Internal 8 MHz RC oscillator (IRC8M).
32,768 Hz Low Speed crystal oscillator (LXTAL).
Internal 40KHz RC oscillator (IRC40K).
PLL clock source can be HXTAL or IRC8M.
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 3 to 25 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 5-3. HXTAL clock source
OSCIN
OSCO UT
C1
C2
Cryst al
The HXTAL crystal oscillator can be switched on or off using the HXTALEN bit in the Control