Chapter5 SignalConnections
©NationalInstruments Corporation 5-9 7344/7334Hardware User Manual
Caution Useo f an unshielded cable can permit noise to corrupt the encoder signals
resulting inlost counts and reduced motion system accuracy.
Encoder Input Circuit
Figure5 -4 showsa simplified s chematic diagram of thecircuit u sedf or
the Phase A, Phase B, and Index encoder inputs. Both phases A and B are
requiredfor proper encoder counter operation, and the signals must su pport
the 90°phase difference within system tolerance. The encoder and Index
signals are conditioned by a software-programmable digital filter inside
the FPGA. The Index signal is optional but highly recommended and
required for initialization functionality with the Find Index function.
Figure5-4. EncoderInput Circuit
TriggerInputs, Shutdown Input, and Breakpoint Outputs
The 7344/7334 controller offers additional high-performance features in
theencoder FPGA. The encoder channels have high-speed position capture
trigger inputs and breakpoint outputs. These signals are useful for
high-speed synchronization of motion with actuators, sensors, and other
partso f the complete motion system:
•TriggerInput <1..4>—When enabled, an active transition on a
high-speed position capture input causes instantaneous position
capture (<100 ns latency)of the corresponding encoder count value.
Youcan use this high-speed position capture functionality for
applications ranging from simple position tagging of sensor data
to complexcamming systems with advance/retard positioning and
registration.An available 7344/7334 controller position mode is to
movean axis Relative to Captured Position.
The polarity of the trigger input is programmable in software as
active-low(inverting) or active-high (non-inverting), rising or falling
74HC244
1k
Ω
1/8W
Fromthe external
connector
encoderinput
pins
Tothe quadrature
decodercircuit
DGND
Vcc
3.3kΩ