Figure 65. X1 Encoding
Ch A
Ch B
Counter Value
7
7
6
5
5
6
•
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 the following figure.
Figure 66. X2 Encoding
Ch A
Ch B
Counter Value 5
6
8
9
7
5
6
8
9
7
•
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 the following figure.
Figure 67. X4 Encoding
Ch A
Ch B
Counter Value
5
6
8
9
10
10
11
11
12
12
13 13
7
5
6
8
7
9
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.
Channel Z behavior—when it goes high and how long it stays high—differs with quadrature
encoder designs. You must refer to the documentation for your quadrature encoder to obtain
timing of channel Z with respect to channels A and B. You must then ensure that channel Z is
high during at least a portion of the phase you specify for reload. For instance, in the image
below, channel Z is never high when channel A is high and channel B is low. Thus, the reload
must occur in some other phase.
In the following figure, the reload phase is when both channel A and channel B are low. The
reload occurs when this phase is true and channel Z is high. Incrementing and decrementing
takes priority over reloading. Thus, when the channel B goes low to enter the reload phase, the
increment occurs first. The reload occurs within one maximum timebase period after the
cRIO-904x User Manual
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© National Instruments
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