Chapter5 SignalConnections
7344/7334Hardware User Manual 5-6 ni.com
Youcan use software disabled limit and home inputs as general-purpose
inputs. Youcan read the status of these inputs at any time and set and
changetheir p olarity as required.
Limit and home inputs are a per axis enhancement on the 7344/7334
controllers and are not required for basic motion control. These inputs
are part of a system solution for complete motion control.
Wiring Concerns
Cautions Forthe end of travel limits to function correctly, the forward limit must be
located att he forwardor positive end of travel and the reverse limit at the negative end
oftravel. Failure to do so 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.
Keeplimit and home switch signals and the irgroun dco nnections wired separately from
themotor driver/amplifier signal and encoder signal connections. Wiring these signals near
each othercan cause faulty motion system operation due to signal noise and crosstalk.
Limit and Home Input Circuit
All limit and home inputs are digitally filtered and must be active for at
least1 ms. 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.
Figure5-2. Limitand Home Input Circuit
Caution Excessiveinput voltages can cause erroneous operation and/or component
failure.Verify that your input voltage is within the specification range.
74HC244
1kΩ
1/8W
Fromthe external
connectorlimit
andhome switch pins
Tothe limit and home
switchcircuits
DGND
Vcc
3.3kΩ