External oscillator, no. Uses only internal oscillator as a system clock.
I just figure it out. bit 6 is Read only, I overlooked this thing in datasheet.
After reset the internal oscillator is enabled and therefore bit 7 of OSCICN is set automatically, therefore its an option to set, the only bit I have to configure is bit 1-0 the option to choose whether to run the clock to its maximum or less or to its minimum.