Chapter 5
Signal Connections
5-6
ni.com
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 7340 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 5-2 shows a simplified schematic diagram of
the circuit used by the limit and home switch inputs for input signal
buffering and detection.
