what is the red 'x' in the schematic?

[J.Kwon]

I don't think it means cut..

[bjorn-spockeli]

The meaning is the same, i.e. it's not connected to VDD.

[J.Kwon]

If so, does not the exteranl crystal oscillator(X1) in the pca10028 work?

[bjorn-spockeli]

@jkwon: It turns out that I was mistaken, the red cross you're referring to, i.e. cross over a connection, means that one or more Electrical Rule check has been suppressed for said connection. You can read more about it [here](techdocs.altium.com/.../Sch_Obj-NoERC((No ERC))_AD

[J.Kwon]

Thank you.