The selectable reference scheme offered by RoboClockII provides the designer with the ability to select between two possible reference sources. This is useful for systems that route a secondary clock source to the system for testing or redundancy purposes. The REF_SEL pin dictates the reference source applied to RoboClockII. If the primary clock goes dead the part will NOT automatically select the secondary source. RoboClockII was specifically designed to provide smooth changeover when swapping between the two reference sources. If the REF_SEL pin is toggled, the part detects this and continues to provide output frequencies identical to the previously locked frequency for a short time. The part will then lock onto the new reference source and smoothly change from the previously locked frequency to the new reference source.