National Instruments Network Adapter NI PXIe-6672, User Manual, Page: 28 / 57

Chapter 3 Hardware Overview
© National Instruments Corporation 3-15 NI PXIe-6672 User Manual
Refer to the Choosing the Type of Routing section for more information
about the synchronization clock.
Note The PXI_Trig/PXI_Star synchronization clock is the same for all routing operations
in which PXI_TRIG <0..7> or PXI_STAR <0..16> is defined as the output, although the
divide-down ratio for this clock (full rate, first divider, second divider) may be chosen on
a per route basis.
Using the PXI Star Triggers
There are up to 17 PXI star triggers per chassis. Each trigger line
is a dedicated connection between the System Timing Slot and one other
slot. The
PXI Specification , Revision 2.1, requires that the propagation
delay along each star trigger line be matched to within 1 ns. A typical upper
limit for the skew in most NI PXI chassis is 500 ps. The low skew of the
PXI star trigger bus is useful for applications that require triggers to arrive
at several modules nearly simultaneously.
The star trigger lines are bidirectional, so signals can be sent to System
Timing Slot from a module in another slot or from System Timing Slot to
the other module.
You can independently select the output signal source for each PXI star
trigger line from one of the following sources:
• PFI <0..5>
• PXI triggers <0..7> (PXI_TRIG <0..7>)
• Another PXI star trigger line (PXI_STAR <0..16>)
• Global software trigger
• PXI_Trig/PXI_Star synchronization clock
• CLKIN
Refer to the Using the PXI Triggers section for more information on the
PXI_Trig/PXI_Star synchronization clock.
Choosing the Type of Routing
The NI PXIe-6672 routes signals in one of two ways: asynchronously or
synchronously. The following sections describe the two routing types and
the considerations for choosing each type.