1. A rotatable downhole assembly adapted for conveying in a borehole and determining a parameter of interest of a medium proximate to the borehole, the downhole assembly comprising: (a) a navigation assembly including a first sensing device including at least one of (i) a gyroscope, (ii) a magnetometer, and, (iii) an accelerometer, for providing a measurement indicative of toolface angle of the downhole assembly, said navigation assembly associated with a first processor; (b) a directional evaluation device for providing measurements indicative of the parameter of interest, said directional evaluation device associated with a second processor; and (c) a common bus operatively connected to the first processor and the second processor.