Chapter 7
Counters
©
National Instruments Corporation
7-15
Figure 7-14 shows a quadrature cycle and the resulting increments and
decrements for X1 encoding. When channel A leads channel B, the
increment occurs on the rising edge of channel A. When channel B
leads channel A, the decrement occurs on the falling edge of
channel A.
Figure 7-14.
X1 Encoding
•
X2 Encoding
—The same behavior holds for X2 encoding except the
counter increments or decrements on each edge of channel A,
depending on which channel leads the other. Each cycle results in
two increments or decrements, as shown in Figure 7-15.
Figure 7-15.
X2 Encoding
•
X4 Encoding
—Similarly, the counter increments or decrements on
each edge of channels A and B for X4 encoding. Whether the counter
increments or decrements depends on which channel leads the other.
Each cycle results in four increments or decrements, as shown in
Figure 7-16.
Figure 7-16.
X4 Encoding
Channel Z Behavior
Some quadrature encoders have a third channel, channel Z, which is also
referred to as the index channel. A high level on channel Z causes the
counter to be reloaded with a specified value in a specified phase of the
quadrature cycle. You can program this reload to occur in any one of the
four phases in a quadrature cycle.
Ch A
Ch B
Co
u
nter V
a
l
u
e
7
7
6
5
5
6
Ch A
Ch B
Co
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nter V
a
l
u
e 5 6
8 9
7
5
6
8
9
7
Ch A
Ch B
Co
u
nter V
a
l
u
e
5 6
8 9 10
10
11 11
12 12
1
3
1
3
7
5
6
8 7
9
