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I was just seeing the datasheet of a motherboard and saw this oscillator circuit:

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What kind of oscillator is this circuit? what are the usage of those resistors?

As you can see it has two input and output(ATI_XTALIN/OUT) that go to the processor but what about MKX1/2?

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Those resistors are zero ohm resistors. If you look closely at the actual board you will probably find that a share of them are not even populated.

This oscillator is a regular crystal oscillator designed to operate at 27MHz.

The zero ohm resistors allow the crystal to be connected to the X1/X2 (XIN/XOUT) pins of two different components. If the ATI_XTAL connections are selected then the crystal will work with that component. It is still possible that the MKX1 could still remain connected (with the MKX2 open) so that device oscillator is excited by the operation of the ATI_XTAL.

It may be that both component oscillators would never be used at the same time based upon the board architecture.

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You will notice that all the resistors there are labelled NC_0_J, which to me reads that these are 0 Ohm resistors (jumpers) so the various board population options and support for various oscillator modes.

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  • \$\begingroup\$ GreatZZZ! that's it! \$\endgroup\$ – Roh Jun 10 '16 at 5:02

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