National Instruments NI 660 Series User Manual page 16

This feature is useful in applications with two or more counters that are
armed by an external start trigger, or that use the same PFI line as a counter
control signal. Pad synchronization is only useful if the counters involved
are using one of the internal timebases. A counter is using maximum
timebase as its source if the synchronous counting mode is enabled for
that counter.
Figures 2-2 and 2-3 illustrate how pad synchronization can be useful.
These figures assume a 0.5 and a 0.75 SOURCE cycle delay between the
PFI 38 input pin, and CTR 0 GATE and CTR 1 GATE, respectively.
Figure 2-2 shows counter 0 at the gate edge on PFI 38 one source period
before counter 1. Figure 2-3 shows both counters at the gate edge on PFI 38
at the same time.
Figure 2-2. Counter 0 at Gate Edge on PFI 38 One Source Period before Counter 1
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Counter
Source
PFI 38
at Input To ASIC
PFI 38
at CTR 0 GATE
PFI 38
at CTR 1 GATE
Sampled
GATE at Ctr0
Sampled
GATE at Ctr1
2-3
Chapter 2 Device Overview
1/2 Cycles
1/4 Cycle
NI 660x User Manual