Chapter 3
Hardware Overview
NI PXI-6682 Series User Manual
3-18
ni.com
Synchronous Routing
A synchronous routing operation is defined in terms of three signals: a
source, a destination, and a
synchronization clock
. A digital signal comes
in on the source and is propagated to the destination after the edge has been
realigned with the synchronization clock.
Unlike asynchronous routing, the output of a synchronous routing
operation does not directly follow the input after a propagation delay.
Instead, the output waits for the next rising edge of the clock before it
follows the input. Thus, the output is said to be “synchronous” with this
clock.
Synchronous routing can send triggers to several places in the same clock
cycle or send the trigger to those same places after a deterministic skew of
a known number of clock cycles. If a signal arrives at two chassis within
the same clock cycle, each NI PXI-6682 Series module realigns the signal
with the synchronization clock and distributes it to the modules in each
chassis at the same time. Synchronous routing can thus remove uncertainty
about when triggers are received. If the delays through the system are such
that an asynchronous trigger might arrive near the edge of the receiver
clock, the receiver might see the signal in the first clock cycle, or it might
see it in the second clock cycle. However, by synchronizing the signal, you
can eliminate the ambiguity, and the signal will always be seen in the
second clock cycle.
