Using the RTSI feature of National Instruments' E-Series, analog output, counter/timer and 653x digital boards, you can synchronize various types of Data
Acquisition. You can find more about synchronization by searching zone.ni.com with "synchronization". The third hit (Understanding Timing, Triggering and Synchronization) is good presentation that covers several timing issues.
The actual synchronization of NI devices is accomplished via the RTSI bus. PLL just locks a particular oscilator to a reference (does not mandate synchronization.)
For examples of how to synchronize input and output on an E-Series board, search the Developers Zone for "synchronize e-series."
Nick Wilson
Application Engineering
National Instruments
www.ni.com/ask