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AT32F435/437
Series Reference Manual
2022.11.11
Page 69
Rev 2.03
4
Clock and reset manage (CRM)
4.1 Clock
AT32F435/437 series provide different clock sources: HEXT oscillator clock, HICK oscillator clock, PLL
clock, LEXT oscillator and LICK oscillator.
Figure 4-1 AT32F435/437 clock tree
USB Divider
/1,1.5,2,2.5,
3,3.5,4,...,7
HICK_TO_USB
USB48M
To USB interface
/2,3,4,...31
RTCCLK
To RTC
LICK RC
40 kHz
RTCSEL[1:0]
LICK
To WDT
WDTCLK
CLKOUT1
Divider1
/1,2,
,5
CLKOUT1
HICK
LEXT
HEXT
PLLCLK
CLKOUT1_SEL
ADC Divider
/2,3,4,...,17
To ADC1,2,3
ADCCLK
Max.80 MHz
Peripheral
clock enable
To AHB peripheral/memory
MACTXCLK
MII_RMII_SEL
EMAC_MII_TX_CLK
EMAC_MII_RX_CLK
0
1
0
1
/2,20
MII_RMII_SEL
To EMAC
To EMAC
EMACRMIICLK
MACRXCLK
ACC
HICK RC
48 MHz
/6
HICK48M
HICKDIV
HEXT_OUT
HEXT_IN
HEXT OSC
4-25 MHz
HEXT
HEXT
PLLRCS
PLLCLK
PLLCLK
LEXT OSC
32.768 kHz
LEXT_IN
LEXT_OUT
LEXT
HICK_TO_SCLK
SCLKSEL
CFD
HICK8M
HEXT
HICK
SCLK
Max.
288 MHz
12S1/2/3/4 CLK
Peripheral
clock enable
AHB
Divider
/1,2...512
HCLK
Max.
288MHz
CPU FCLK
/8
CPU SysTick
MII_RMII_SEL
To EMAC
CLKOUT1
Divider2
/1,2..512
CLKOUT2
Divider1
/1,2,
,5
CLKOUT2
HEXT
PLLCLK
CLKOUT2_SEL1
CLKOUT2
Divider2
/1,2..512
SCLK
HICK
ADCCLK
USB48M
CLKOUT2_SEL2
LICK
LEXT
DVP_PCLK
/MS
VCO
xNS
/FR
Peripheral
Clock enable
PCLK1/2
Max.
144 MHz
to APB1/2
peripheral
Max.
288MHz
to TMRx
CLK
Peripheral
clock enable
APB1/2
Divider
/1,2,4,8,16
x1,x 2
AHB, APB1 and APB2 all support multiple frequency division. The AHB domain has a maximum of 288
MHz, and both APB1 and APB2 are up to 144 MHz.
4.1.1
Clock sources
High speed external oscillator (HEXT)
The HEXT includes two clock sources: crystal/ceramic resonator and bypass clock.
The HEXT crystal/ceramic resonator is connected externally to a 4~25 MHz HEXT crystal that produces
a highly accurate clock for the system. The HEXT clock signal is not released until it becomes stable.
An external clock source can be provided by HEXT bypass. Its frequency can be up to 25 MHz. The
external clock signal should be connected to the HEXT_IN pin while the HEXT_OUT pin should be left
floating.
High speed internal clock (HICK)
The HICK oscillator is clocked by a high-speed RC in the microcontroller. The internal frequency of the
HICK clock is 48 MHz. Although it is less accurate, its startup time is shorter than the HEXT crystal
oscillator. The HICK clock frequency of each device is calibrated by ARTERY to 1% accuracy (25°C) in
factory. The factory calibration value is loaded in the HICKCAL[7: 0] bit of the clock control register. The
RC oscillator speed may be affected by voltage or temperature variations. Thus the HICK frequency can
be trimmed using the HICKTRIM[5: 0] bit in the clock control register.
The HICK clock signal is not released until it becomes stable.
PLL clock