NI C Series Getting Started

X2 Encoding
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 20. X2 Encoding
Encoder Count
Ch A
Ch B
5 6 87 9 9 8 67 5
X4 Encoding
The counter increments or decrements on each edge of channels A and B. 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 21. X4 Encoding
Encoder Count
Ch A
Ch B
5 6 87 9 10 11 12 13 13 12
10
11 9 8 7 6 5
Channel Z
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. Depending on
configuration, this reload can 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-diers with
quadrature encoder designs. 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.
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. Thus, when
© National Instruments
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NI-9361 Getting Started

NI C Series Specifications

General

Brand	NI
Model	C Series
Category	Control Unit
Language	English