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Chapter 7 Counters
© National Instruments Corporation 7-17 NI 6238/6239 User Manual
Figure 7-15. 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 7-16.
Figure 7-16. 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 7-17.
Figure 7-17. 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
Counter Value
7
7
6
5
5
6
Ch A
Ch B
Counter Value
56 8
9
7
5
6
8
9
7
Ch A
Ch B
Counter Value 5 6 8 9 10 1011 1112 1213 137
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