www
.mcu.com.cn
34
/
239
Rev.
1.00
CMS80F731x Reference Manual
4.
Clock Structure
There are four types of clock sources for system clocks, and clock source and clock divider can be selected by setting the
system configuration register or user register. The system clock sources are as follows:
◆
Internal high-speed oscillation HSI (48MHz).
◆
External high-speed crystal oscillation HSE (8MHz/16MHz).
◆
External low-speed crystal oscillation LSE (32.768KHz).
◆
Internal low-speed oscillation LSI (125KHz).
The default clock source of the chip is HSI, and the system clock runs at HSI after the chip reset is complete. If you need
to change the system clock source, you can set the system configuration register (with the programming tool and host computer
software), or through the user register configuration (follow the procedure to set the relevant register, as detailed below). When
using external high-speed and low-speed oscillators as the system clock, the oscillation stop monitoring function is supported,
as detailed below.
4.1
System Clock Structure
The system clock block diagram of each peripheral module is shown in the following figure:
HSI
oscillator4
8MHz
Regist er
CLKDI V
BUZZ
ADC
PWM
IIC
SPI
WDT
TIMER0/ 1
TIMER2
TIMER3/ 4
BRT
BOOT
CRC
UART0
LED
Fsys
Fsys_pre
Fosc
LSI
oscillator
125KHz
HSE/ LSE
GATE
GATE
MUX
MUX
LSE
LSI
OSCI N
OSCOUT
LSE
HSE
LSI
HSI_FS
CPU
CONFIG
configuration
/register
configuration
MUX
CONFIG
configuration
MUX
/2
/1
/8
/4
CONFIG
configuration
MUX
/2
/1
/6
/3
UART1
MUX
SCM
MUX
LSE
HSE
LSI
LSE
Timer
LSE
WUT
LSI
TOUCH
Touch
Oscillator
8MHz
MUX