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Chapter 5
Counters
80 MHz Source Mode
In 80 MHz source mode, the chassis synchronizes signals on the rising edge of the source, and
counts on the third rising edge of the source. Edges are pipelined so no counts are lost, as shown
in Figure 5-38.
Figure 5-38.
80 MHz Source Mode
External or Internal Source Less than 20 MHz
With an external or internal source less than 20 MHz, the module generates a delayed Source
signal by delaying the Source signal by several nanoseconds. The chassis synchronizes signals
on the rising edge of the delayed Source signal, and counts on the following rising edge of the
source, as shown in Figure 5-39.
Figure 5-39.
External or Internal Source Less than 20 MHz
8
0 MHz
S
o
u
rce
S
ynchronize
Co
u
nt
S
o
u
rce
Del
a
yed
S
o
u
rce
S
ynchronize
Co
u
nt
