National Instruments PXI-7340, User Manual And Specifications

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Chapter 4 Signal Connections
The input polarity of these signals is software programmable for active-low (inverting) or
active-high (non-inverting).
You can use software disabled limit and home inputs as general-purpose inputs. You can read
the status of these inputs at any time and set and change their polarity as required.
Limit and home inputs are a per axis enhancement on the NI 7340 motion controller and are not
required for basic motion control. These inputs are part of a system solution for complete motion
control.
Caution National Instruments recommends using limits for personal safety, as well
as to protect the motion system.
Wiring Concerns
For the end of travel limits to function correctly, the forward limit must be located at the forward
or positive end of travel, and the reverse limit at the negative end of travel.
Caution Failure to follow these guidelines may result in motion that stops at, but
then travels through, a limit, potentially damaging the motion system. Miswired
limits may prevent motion from occurring at all.
Keep limit and home switch signals and their ground connections wired separately from the
motor driver/amplifier signal and encoder signal connections.
Caution Wiring these signals near each other can cause faulty motion system
operation due to signal noise and crosstalk.
Limit and Home Input Circuit
By default, all limit and home inputs are digitally filtered and must be active for at least 1 ms.
You can use MAX to disable digital filtering for limit and home inputs. Figure 4-3 shows a
simplified schematic diagram of the circuit used by the limit and home switch inputs for input
signal buffering and detection.
Figure 4-3. Limit and Home Input Circuit
74FCT244
1 k Ω
1/ 8 W
From the extern a l
connector limit
a nd home s witch pin s
To the limit a nd home
s witch circ u it s
DGND
Vcc
3 . 3 k
Ω