Chapter 4
Signal Connections
©
National Instruments Corporation
4-11
Encoder Input Circuit
The PCI-7390 provides optically isolated, RS-422 compatible differential
encoder inputs. Figure 4-6 shows a simplified schematic diagram of the
encoder input interface circuit. You can connect these inputs to RS-422
driver outputs or to single-ended sourcing or sinking outputs that meet
the voltage and current requirements. Figures 4-7 and 4-8 show the
connections to devices with sinking outputs and sourcing outputs,
respectively. Both phases A and B are required for proper encoder counter
operation. The encoder and Index (Phase Z) signals are conditioned by a
software-programmable digital filter inside the FPGA. The Index
(Phase Z) signal is optional but highly recommended in combination with
Find Reference moves for more accurate positioning.
Figure 4-6.
Encoder Input Circuit
Figure 4-7.
Encoder Input Circuit Connected to a Sinking Output Device
with a +24 V Power Supply
High Speed Optocoupler
V
cc
R
LIMIT
PCI-7390
Encoder–
Input
Input
PCI-7390
Output
V+
V–
High Speed Optocoupler
V
cc
R
LIMIT
R
EXT
Encoder–
Input
Input
Encoder with
Sinking Output
Isolated Ground
Isolated Ground
2 k
Ω
+24 V
