©
National Instruments Corporation
15
MID-7604/7602 Stepper Power Motor Drive User Guide
The MID-7604/7602 supports differential inputs for Phase A, Phase B, and Index signals. You can easily
accommodate encoders with various phase relationships by swapping the signals and/or connecting
them to the inverting inputs as specific applications require. The Index signal must occur when both
Phase A and Phase B signals are low, as shown in Figure 7. If the Index polarity is inverted, try reversing
the Index and Index signals on differential encoders or using the Index input on single-ended encoders.
Figure 7 shows the proper encoder phasing for CW (forward) motor rotation.
Figure 7.
Encoder Signal Phasing, CW Rotation
Closed-loop stepper applications require consistent directional polarity between the motor and encoder
for correct operation. The National Instruments motion control standard directional polarity is as
follows:
•
Positive = forward = clockwise (CW) facing motor shaft
•
Negative = reverse = counter-clockwise (CCW) facing motor shaft
Figure 8 shows clockwise and counter-clockwise motor rotation.
Figure 8.
Clockwise and Counter-Clockwise Motor Rotation
Ph
as
e A
Ph
as
e B
Index
CCW
CW
