The backplane synchronization clock may be any of the following signals.
•
Clock Generation
•
PXI_CLK10
•
PXIe_CLK100
•
OCXO
•
CLKIN
•
Any of the previously listed signals divided by the first frequency divider (2
n
, up to 512).
•
Any of the previously listed signals divided by the second frequency divider (2
m
, up to
512).
Refer to the
section for more information about the
synchronization clock.
Note
The backplane synchronization clock is the same for all routing operations in
which PXI_TRIG<0..7>, PXIe_DSTARB<0..16>, 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 Express 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 the system timing slot from a
module in another slot or from the 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>
•
PFI_LVDS<0..2>
•
PXI triggers <0..7> (PXI_TRIG<0..7>)
•
Another PXI star trigger line (PXI_STAR<0..16>)
•
Global software trigger
•
Backplane synchronization clock
•
PXIe_DSTARC
•
Steady logic high or low
Refer to the
section for more information on the backplane
synchronization clock.
Using the PXIe_DSTARB and PXIe_DSTARC Triggers
To improve beyond the performance the PXI Star triggers offer in low skew trigger routing,
PXI Express implements PXIe_DSTARB and PXIe_DSTARC triggers. Each PXI Express
peripheral slot in a PXI Express chassis has independent PXIe_DSTARB and PXIe_DSTARC
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PXIe-6674T User Manual
