National Instruments NI PCI-5911 - Manual (Page 27)

Chapter 2 Hardware Overview
© National Instruments Corporation 2-13 NI PCI-5911 User Manual
route that trigger over the RTSI bus to trigger the other digitizer(s).
However, the trigger that is routed to the other digitizer(s) is sent
synchronously to an internal 25 MHz clock. For more information about
synchronization, refer to the NI-SCOPE Software User Manual.