Stm32 clock Analysis

In stm32, there are four clock sources: Hsi, HSE, LSI, LSE, And a pll output

1,HSIIt is a high-speed internal clock, RC oscillator, and the frequency is 8 MHz.

2,HSEIt is a high-speed external clock, which can be connected to a Z/Ceramic Resonator or an external clock source. The frequency range is 4 MHz ~ 16 MHz.

3,LSIIt is a low-speed internal clock, RC oscillator, and the frequency is 40 kHz.

4,LSEIt is a Z crystal with a low-speed external clock and a connection frequency of 32.768khz.

5,PLLThe clock input source can be HSI/2, HSE or HSE/2. The multiplier value can be 2 ~ 16 times, but its output frequency cannot exceed 72 MHz.

 

If the external crystal oscillator is not used on the stm32, the method of connecting osc_in and osc_out is as follows:

1. for products with 100 or 144 feet, osc_in should be grounded and osc_out should be suspended.

2. There are two methods for connecting products with less than 100 feet:

1. osc_in and osc_out are grounded by a 10 k resistor, respectively. This method improves EMC performance.

2. remap osc_in and osc_out to pd0 and pd1 respectively, configure pd0 and pd1 as the push-pull output and output '0 '. This method reduces power consumption and saves two External Resistors (2.1 relative to the above.