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As a preface, I've seen this question and I do need an accurate clock.


So I'm designing a board that uses an STM32F030C8T6. I think I've got the VDD/VSS pins all sorted, and next on my agenda is the oscillator.

I've selected an CL10C180JB8NNNC 8MHz Crystal Oscillator as it's a basic part on JLPCB and good enough for what I need.

I've never added a crystal oscillator to a board that I've designed before, but I think this is correct.

Oscillator Subcircuit

So my first question is, have I done this right?

My second question is whether I need to be adding this oscillator to the XXXX-OSC32_XX pins or the XXX-OSC-XX pins or both.

I have looked at the datasheet but I can't seem to find a good explanation of what's going on here (although it's very possible I've missed something here).

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3 Answers 3

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I'd like to thank DKNguyen as his answer pointed me in the right direction.


Looking at sections 6.2.1 (HSE Clock) and 6.2.5 (LSE Clock) of the reference manual it would seem as though my original implementation is wrong.

The OSC32_XX pins seem as though they're for the low-frequency oscillator that powers the RTC.

The OSC_XX pins are used to generate a rate on the main clock (what I want).

The actual circuitry, however, does seem to be implemented correctly, I just need to change the pins that its connected to.

App Note

enter image description here

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The way ST organizes their information for the microcontrollers is as follows:

  • The Datasheet only provides package specific information like pinouts. You want to look at the user reference manual for usage information that is general to parts that share the same family (core and peripherals). The only time you need to refer to the datasheet is for pinouts and electrical characteristics. Otherwise the datasheet is basically a marketing document that just lists a high-level description of the peripherals, not how to use them.
  • For usage information that is shared amongst a family or subfamily you need to look at the User Reference Manual. This contains things such as how to use the peripherals and their registers. Normally this grouped into numbers such as STM32G4, STM32F3, STM32F7, or STM32H7. Sometimes it goes one digit lower when they introduce new members to family with extra peripherals so make sure you aren't doing something like using the manual for the STM32H7xx when you should actually be using the manual for the STM3272x.
  • ST also has app notes for using peripherals. You generally don't need these and they are not overly specific to parts but if you're really stuck they can help. One does exist for the oscillator: AN2867
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  • \$\begingroup\$ Hi, thanks for the answer, although, whilst helpful, I don't think it directly answers my question. I've actually seen AN2867 but it doesn't help as far as the pin issue is concerned, I'll have a read through the reference manual for STM32F0s and see if that helps more \$\endgroup\$ Sep 17, 2022 at 16:59
  • \$\begingroup\$ @ScottishTapWater The app notes are usually only helpful when you have no idea what you're actually looking at. They're more like guides than manuals. They won't list part specific information except maybe for the part they are using as an example. You'll still need to go to the user reference manual for that. \$\endgroup\$
    – DKNguyen
    Sep 17, 2022 at 17:03
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The oscillator is connected to wrong pins on the MCU. Change them from the 32 kHz LSE oscillator pins to the main HSE oscillator pins.

The circuit topology is basically correct, but the actual crystal parameters are unknown. You linked to a datasheet that is generic for a series of crystals, not an individual crystal part number you can buy.

So it is unknown if the capacitor values are correct, or if the crystal requires a series resistance for limiting drive level.

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  • \$\begingroup\$ This is the oscillator jlcpcb.com/partdetail/YangxingTech-X49SM8MSD2SC/C12674 \$\endgroup\$ Sep 17, 2022 at 18:51
  • \$\begingroup\$ @ScottishTapWater The 20pF CL specification sounds a bit high, if not too high. Do the math in the crystal selection appnote to figure it out if the crystal is suitable or unsuitable. For what use you need the crystal? \$\endgroup\$
    – Justme
    Sep 17, 2022 at 20:53

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