National Instruments PCI-6601, User Manual

Page: 19 / 52

Chapter 2 Device Overview
NI 660x User Manual 2-6 ni.com
Example Application That Works Incorrectly (Duplicate Counting)
In Fig
u
re 2-5, after the first rising edge of Gate, no So
u
rce p
u
lses occ
u
r.
So the co
u
nter does not write the correct data to the b
u
ffer.
Figure 2-5. Example Application That Works Incorrectly
Example Application That Prevents Duplicate Counting
With d
u
plicate co
u
nt prevention enabled, the co
u
nter synchronizes
both the So
u
rce and Gate signals to the maxim
u
m onboard timebase.
By synchronizing to the timebase, the co
u
nter detects edges on the Gate
even if the So
u
rce does not p
u
lse. This enables the correct c
u
rrent co
u
nt to
be stored in the b
u
ffer even if no So
u
rce edges occ
u
r between Gate signals.
Fig
u
re 2-6 shows an example application that prevents d
u
plicate co
u
nting.
Figure 2-6. Example Application That Prevents Duplicate Counting
Gate
Source
Counter Value
Buffer
7
6 7 1
No Source edge, so no
value written to buffer.
Gate
Source
80 MHz Timebase
Counter Value
Buffer
0
7 7
6 7 0 1
Counter detects
rising Gate edge. Counter value
increments only
one time for each
Source pulse.