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I'm trying to set up an HSE for my STM32f4, using this crystal. but there are 2 pins: OSC_IN and OSC_OUT, but my crystal only has one output.

What do I link OSC_IN and OUT to? enter image description here

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  • \$\begingroup\$ Try here stm32f4-discovery.com \$\endgroup\$
    – Laki
    Commented Jun 2, 2015 at 14:10
  • \$\begingroup\$ Why do you have that 15pF cap on the output of your oscillator? \$\endgroup\$
    – EM Fields
    Commented Jun 2, 2015 at 15:23
  • \$\begingroup\$ The 15 pF is not needed since it is what the oscillator is capable of driving (15-50pF). \$\endgroup\$ Commented Jun 2, 2015 at 18:59

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The 'crystal' you are using is actually a complete oscillator module that generates a CMOS (digital) output pulse. The two pins on the STM32 are for when you are using a bare crystal and provide access points to the built-in oscillator circuit.

As you don't need to use this you can just connect the output from your oscillator to the OSC_IN pin and leave the OSC_OUT disconnected. Note that it is very important that you configure the chip to use an external clock - not the HSE oscillator - or it won't work properly.

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    \$\begingroup\$ In STs words it's commonly called HSE bypass. \$\endgroup\$
    – Arsenal
    Commented Jun 3, 2015 at 6:45

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