I am designing a PCB for a project. On the PCB, I plan on using the STM32F030C8T6 microcontroller. The resulting board does not need to do many tasks. I need the design to be able to do the following:

  1. Communicate via I2C.
  2. Allow for programming via SWD.
  3. Switch some LED's on and off.

Would I need to include an external oscillator in my PCB design? Thank you for your time.


2 Answers 2


I2C and SWD both carry their own clock so there will not be any synchronization issues if the clock is not accurate.

This means it is safe to use the internal oscillators, but they do use a bit more energy.


The controller has an internal 8MHz RC oscillator, as well as an optional PLL. If you do not need an accurate clock, you can run the controller without an external oscillator. All of its integrated peripherals will function just fine (if you can tolerate a possibly inaccurate operating frequency).

  • \$\begingroup\$ I believe I2C does not require an external clock, my main concern is whether SWD would, require an external clock or not. \$\endgroup\$ Aug 27, 2021 at 7:38
  • \$\begingroup\$ You can run all of the controller's interfaces without an external clock. I2C, SWD, SPI, UART - whatever you like. \$\endgroup\$ Aug 27, 2021 at 7:40
  • 2
    \$\begingroup\$ @JonatanS. Sure you can use them with internal clock but it does not guarantee if it will work. The internal oscillators have accuracy of +/- 5 % over temperature range, and that is too much for an UART to work. \$\endgroup\$
    – Justme
    Aug 27, 2021 at 8:34

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