Chapter 5
Signal Connections
5-10
ni.com
Figure 5-4.
Encoder Input Circuit
Trigger Inputs, Shutdown Input, and Breakpoint Outputs
The 7340 offers additional high-performance features in the encoder
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 parts of the
complete motion system:
•
Trigger Input <1..4>—When enabled, an active transition on a
high-speed position capture input causes instantaneous position
capture of the corresponding encoder count value. You can use this
high-speed position capture functionality for applications ranging
from simple position tagging of sensor data to complex camming
systems with advance/retard positioning and registration. An available
7340 position mode is to move an 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
edge. You also can use a trigger input as a latching general-purpose
digital input by simply ignoring the captured position.
•
Shutdown Input—When enabled in software, the shutdown input
signal can be used to kill all motion by asserting the controller inhibits,
setting the analog outputs to 0 V, and stopping any stepper pulse
generation. To activate shutdown, the signal must transition from a low
to a high state, or rising edge.
•
Breakpoint Output <1..4>—A breakpoint output can be programmed
to transition when the associated encoder value equals the breakpoint
position. You can use a breakpoint output to directly control actuators
or as a trigger to synchronize data acquisition or other functions in the
motion control system.
74FCT244
1 k
Ω
1/8 W
From the external
connector
encoder input
pins
To the quadrature
decoder circuit
DGND
Vcc
3.3 k
Ω