Specifies or returns the synchronization clock source for the rear zone (PXI_Trig, PXI_Star, and PXIe_DStarB) terminals.
NISYNC_VAL_PFI0
NISYNC_VAL_CLK10
NISYNC_VAL_DDS
NISYNC_VAL_CLK100
NISYNC_VAL_CLKIN
NISYNC_VAL_OSCILLATOR