EXTERNAL OSCILLATOR

[rohithinthingstech]

 I AM USING STM32F407G-DISC1 BOARD FOR DEVELOPING CUSTOM BOARD.HERE AN OSCILLATOR IS CONNECTED TO PH1 AND PH2 PINS. IS IT IS COMPALSORY FOR DEVELOPING CUSTOM BOARD?

[unsigned_char_array]

From the datasheet:

Clock, reset and supply management:

• 1.8 V to 3.6 V application supply and I/Os
• POR, PDR, PVD and BOR
• 4-to-26 MHz crystal oscillator
• Internal 16 MHz factory-trimmed RC (1% accuracy)
• 32 kHz oscillator for RTC with calibration
• Internal 32 kHz RC with calibration

STM32 MCUs always boot with the internal 16MHz oscillator and in the system init the optional external oscillators and the internal PLLs can be turned on.
If the accuracy of the internal oscillator is good enough for your application you do not need an external crystal or oscillator. If it is not accurate enough you may need to do some calibration or opt for an external crystal or oscillator.
If you decide to use a crystal be sure to check the load capacitance of the crystal as the maximum drive strength of the MCU oscillator pins may not be strong enough to drive the crystal. This depends on the family of the MCU. Set the drive strength to the proper level with STM32CubeMX.

[Andrew Neil]

PLEASE DON'T SHOUT!

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@rohithinthingstech wrote:AN OSCILLATOR (sic) IS CONNECTED TO PH1 AND PH2 PINS. 

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No, that's not an oscillator - that is just a crystal.

See: https://community.st.com/t5/stm32-mcus-products/stm32f4-osc-problem/m-p/664136/highlight/true#M241592

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@rohithinthingstech wrote:

IS IT IS COMPALSORY FOR DEVELOPING CUSTOM BOARD?

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No - as @unsigned_char_array explained, it depends on the requirements of your particular application.

You should also study Application note AN4488, Getting started with STM32F4xxxx MCU hardware development:

https://www.st.com/resource/en/application_note/an4488-getting-started-with-stm32f4xxxx-mcu-hardware-development-stmicroelectronics.pdf

Probably also worth reviewing the other Application Notes available on the STM32F407VG Product Page:

https://www.st.com/en/microcontrollers-microprocessors/stm32f407vg.html#documentation