Chapter 5 Signal Connections
© National Instruments Corporation 5-7 NI 7350 User Manual
Limit and home inputs are digitally filtered and must remain active for at
least 1 ms to be recognized. Refer to Appendix A, Specifications, for more
information. You can use MAX to disable digital filtering for limit and
home inputs. Active signals should remain active to prevent motion from
proceeding further into the limit. Pulsed limit signals stop motion, but they
do not prevent further motion in that direction if another move is started.
The input polarity of these signals is software programmable for active low
or active high.
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 7350
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. Limits that are wired
incorrectly may prevent motion fromoccurring at all.
Keep limit and home switch signals and their ground connections wired
separately from the motor drive/amplifier signal and encoder signal
connections.
Caution Wiring these signals near each other can cause faulty motion system operation
that is due to signal noise and crosstalk.
Limit and Home Input Circuit
Limit and home inputs have an onboard pull-up resistor. If left floating, the
inputs are interpreted as a high logic level.