Embedded Systems: Clocks

Clock System

The heart of the MCU, any device must be driven by a clock to start working

• The clock signal is generated by the oscillation of the quartz crystal oscillator

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(1) Clock source classification

1. External clock source

(1) External high-speed crystal oscillator

• HFXTCLK: High-frequency oscillator

(2) External low-speed crystal oscillator

• LFXTCLK: Low-frequency oscillator

2. Internal clock source

(1) Internal high-speed crystal oscillator

• DCO: Internal digitally controlled oscillator that can output clocks of different frequencies (equivalent to a multiplier phase-locked loop)
• MODCLK: Internal low-power oscillator
• SYSOSC: Internal oscillator

(2) Internal low-speed crystal oscillator

• REFOCLK: Internal, low-power low-frequency oscillator
• VLOCLK: Internal very-low-power low-frequency oscillator

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(2) Clock configuration process

1. Clock source selection

2. Clock Multiplier (if necessary)

3. Clock division

Different peripherals can choose different clock systems, please refer to the relevant device data sheet for details

Some clock sources may have limitations, and under this clock source, the system power and Flash read speed may need to be changed

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