Crystal Oscillator step by step activation and testing. STM32F405

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July 5, 2019
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Is there a document outlining how to power and test the crystal oscillator from ST? STM32F405

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Best answer by waclawek.jan

Read the RCC chapter of RM0090.

You enable HSE by setting RCC_CR.HSEON, and then wait until RCC_CR.HSERDY is set, indicating the HSE is up and running.

A similar procedure is for LSE; its respective bits are in RCC_BDCR.

For checking, you can output HSE onto MCO1 or MCO2, see RCC_CFGR.MCO1 and RCC_CFGR.MCO2 (you may need to set the respective GPIOx_OSPEEDR to some of the higher settings).

Note, that if you want to probe on the crystal directly, you need a high-impedance oscilloscope probe (1:10 or an active one). LSE is a low-power oscillator and probing it may stop the oscillations entirely.

JW

waclawek.janBest answer

Super User

Read the RCC chapter of RM0090.

You enable HSE by setting RCC_CR.HSEON, and then wait until RCC_CR.HSERDY is set, indicating the HSE is up and running.

A similar procedure is for LSE; its respective bits are in RCC_BDCR.

For checking, you can output HSE onto MCO1 or MCO2, see RCC_CFGR.MCO1 and RCC_CFGR.MCO2 (you may need to set the respective GPIOx_OSPEEDR to some of the higher settings).

Note, that if you want to probe on the crystal directly, you need a high-impedance oscilloscope probe (1:10 or an active one). LSE is a low-power oscillator and probing it may stop the oscillations entirely.

JW