National-instruments Data Acquisition Device NI USB-621x Manual de usuario descargar pdf (Pagina 109)

Chapter 8 Counters

NI USB-621x User Manual 8-16 ni.com

Figure 8-14. X1 Encoding

• X2 Encoding—The same behavior for X1 encoding 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 8-15.

Figure 8-15. 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 8-16.

Figure 8-16. 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.

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

Ch A

Ch B

Counter Value

Ch A

Ch B

Counter Value

56 8

Ch A

Ch B

Counter Value 5 6 8 9 10 10 11 11 12 12 13 13 7

5 6 8 7 9

1 2 ... 104 105 106 107 108 109 110 111 112 113 114 ... 184 185

Sin comentarios

National-instruments Data Acquisition Device NI USB-621x Manual de usuario Pagina 109