National Instruments 7340 PCI Benutzerhandbuch

Figure 5-4.  Encoder Input Circuit

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