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GD32E23x User Manual
74
Figure 4-2. Clock tree
/2
4-32 MHz
HXTAL
8 MHz
IRC8M
×2,3,4
…
,32
PLL
Clock
Monit or
PLLSEL
PREDV
PLLMF
0
1
00
01
10
CK_IRC8M
CK_HXTAL
CK_PLL
CK_SYS
72 MHz max
AHB
Prescaler
÷
1,2...512
CK_AHB
72 MHz max
APB1
Prescaler
÷
1,2,4,8,16
APB2
Prescaler
÷
1,2,4,8,16
CK_APB2
72 MHz max
Peripheral enable
PCLK2
to APB2 peripherals
CK_APB1
72 MHz max
Peripheral enable
PCLK1
to APB1 peripherals
TIMERx
enable
CK_TIMERx
to TIMER0,14,15,16
TIMERx
enable
CK_TIMERx
to TIMER2,5,13
AHB enable
HCLK
(to AHB bus,Cortex-M23,SRAM,DMA)
FMC enable
(by hardware)
CK_FMC
(to FMC)
÷8
CK_CST
(to Cortex-M23 SysTick)
FCLK
(free running clock)
32.768 KHz
LXTAL
11
10
01
40 KHz
IRC40K
CK_RTC
CK_FWDGT
(to RTC)
(to FWDGT)
/32
CK_ LXTAL
CK_PLL
CK_HXTAL
CK_IRC8M
CK_OUT
SCS[1:0]
RTCSRC[1:0]
÷1,2.
..16
CK_I2S
(to I2S)
CK_SYS
CK_IRC40K
CK_IRC28M
0
/1,2
÷1,2,4...128
CKOUTDIV[2:0]
FMC
CKOUTSEL[2:0]
IRC
CK
XTAL
_
CK_
_
CK SYS
10
01
00
M
8
L
11
CK USART
_
0
0
to USART
28 MHz
28M
IRC
CK_ ADC to ADC
28 MHz max
ADCSEL
1
0
ADC
Prescaler
÷
,
3 5 ,
ADC
Prescaler
÷
,
2 4, ,
6 8
7,9
÷
2
1,
USART0SEL[1:0]
TIMER2,5,13
if(
APB1 prescaler = 1
)
÷1
else
÷
[APB1 prescaler/2]
TIMER0,14,15,16
if(
APB2 prescaler = 1
)
÷1
else
÷
[APB2 prescaler/2]
The frequency of AHB, APB2 and the APB1 domains can be configured by each prescaler.
The maximum frequency of the AHB, APB2 and APB1 domains is 72 MHz/72 MHz/72 MHz.
The Cortex System Timer (SysTick) external clock is clocked with the AHB clock (HCLK)
divided by 8. The systick can work either with this clock or with the AHB clock (HCLK),
configurable in the systick control and status register.
The ADC are clocked by the clock of APB2 divided by 2, 4, 6, 8 or by the clock of AHB
divided by 3, 5, 7, 9 or IRC28M or IRC28M/2 clock for GD32E23x
series selected by
ADCSEL bit in configuration register 2 (RCU_CFG2). The USART0 is clocked by IRC8M
clock or LXTAL clock or system clock or APB2 clock, which selected by USART0SEL bits in
configuration register 2 (RCU_CFG2).
The RTC is clocked by LXTAL clock or IRC40K clock or HXTAL clock divided by 32 which
select by RTCSRC bits in backup domain control register (RCU_BDCTL).
The FWDGT is clocked by IRC40K clock, which is forced on when FWDGT started.
If the APB prescaler is 1, the timer clock frequencies are set to AHB frequency divide by 1.
Otherwise, they are set to the AHB frequency divide by half of APB prescaler.