Chapter 7
Counters
©
National Instruments
7-25
X Series User Manual
the channel B goes low to enter the reload phase, the increment occ
u
rs first.
The reload occ
u
rs within one maxim
u
m timebase period after the reload
phase becomes tr
u
e. After the reload occ
u
rs, the co
u
nter contin
u
es to co
u
nt
as before. The fig
u
re ill
u
strates channel Z reload with X4 decoding.
Figure 7-21.
Channel Z Reload with X4 Decoding
Measurements Using Two Pulse Encoders
The co
u
nter s
u
pports two p
u
lse encoders that have two channels—channels
A and B.
The co
u
nter increments on each rising edge of channel A. The co
u
nter
decrements on each rising edge of channel B, as shown in Fig
u
re 7-22.
Figure 7-22.
Measurements Using Two Pulse Encoders
For information abo
u
t connecting co
u
nter signals, refer to the
Default
Counter/Timer Pinouts
section.
Buffered (Sample Clock) Position Measurement
With b
u
ffered position meas
u
rement (position meas
u
rement
u
sing a
sample clock), the co
u
nter increments based on the encoding
u
sed after the
co
u
nter is armed. The val
u
e of the co
u
nter is sampled on each active edge
of a sample clock. A DMA controller transfers the sampled val
u
es to host
memory. The co
u
nt val
u
es ret
u
rned are the c
u
m
u
lative co
u
nts since the
Ch A
Ch B
Co
u
nter V
a
l
u
e
5
6
A = 0
B = 0
Z = 1
Ch Z
M
a
x Time
bas
e
8
9
0
2
1
7
4
3
Ch A
Ch B
Co
u
nter V
a
l
u
e
2
3
5
4
3
4
4
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