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I am selecting an MCU (EFM8BB10F2G-A-QFN20 Datasheet here) for one of my projects and I found a strange thing. This MCU has only pin for external clock source:

pin config

Till now, I have never encountered this case. In every other MCU I have used, there were two pins for connecting an external crystal. How can I use a crystal in this case?

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  • \$\begingroup\$ While not the case here, there are in fact oscillator circuit topologies which ground one side of the crystal. It's rather rare to use these for an on-chip clock oscillator, but I did once work with such a part - only cannot recall what it specifically was. \$\endgroup\$ – Chris Stratton Sep 1 '18 at 15:54
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You can't (directly). The datasheet clearly states on the first page:

Clock Sources:

• Internal 24.5 MHz oscillator with ±2% accuracy

• Internal 80 kHz low-frequency oscillator

• External CMOS clock option

What you can use is a crystal oscillator (ie. crystal + active circuitry in the same component).

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