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Chapter 3
Hardware Overview
© National Instruments Corporation
3-17
Synchronous Routing
A synchronous routing operation is defined in terms of three signal
locations: 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.
locations: 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.
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.
Figure 3-6 shows a timing diagram that illustrates synchronous routing.
Figure 3-6. Synchronous Routing Operation
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 PXIe-6672 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
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 PXIe-6672 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
Trigger Input
Synchronization
Clock
Trigger Output
Setup
Time
t
setup
Hold
Time
t
hold
Clock to Output
Time, t
Time, t
CtoQ