National Instruments 7334 - Manual (Page 29)

Chapter 5 Signal Connections
7344/7334 Hardware User Manual 5-4 ni.com
Motion Axis Signals
The following signals control the servo amplifier or stepper driver:
• Analog Output <1..4> (7344 only)—These 16-bit DAC outputs are
typically the servo command outputs for each axis. They can drive
the industry-standard ±10 V output, and can be software limited to
any positive or negative voltage range desired. They also feature
a software-programmable voltage offset.
Although typically used as the command output of an axis control
loop, unused DACs can also function as independent analog outputs
for general-purpose control.
• Analog Output Ground (7344 only)—To help keep digital noise
separate from the analog DAC outputs, there is a separate return
connection. You should use this analog ground connection and not
Digital Ground (digital I/O reference) as the reference for the DAC
outputs when connecting to servo amplifiers.
• Axis <1..4> Step (CW) and Dir (CCW)—These open-collector signals
are the stepper command outputs for each axis. The 7344/7334
controller supports both major industry standards for stepper
command signals—step and direction, or independent CW and CCW
pulse outputs.
The output configuration and signal polarity is software programmable
for compatibility with various third-party drives, as follows:
– When step and direction mode is configured, each commanded
step (or microstep) produces a pulse on the step output. The
direction output signal level indicates the command direction of
motion, either forward or reverse.
– CW and CCW mode produces pulses (steps) on the CW output for
forward-commanded motion and pulses on the CCW output for
reverse-commanded motion.
In either case, you can set the active polarity of both outputs to
active-low (inverting) or active-high (non-inverting). For example,
with step and direction, you can make a logic high correspond to either
forward or reverse direction.
The Step (CW) and Dir (CCW) outputs are driven by high-speed
open-collector TTL buffers that feature 64 mA sink current capability
and built-in 3.3 k
Ω pull-up resistors to +5 V.
Caution Do not connect these outputs to anything other than a +5 V circuit. The output
buffers will fail if subjected to voltages in excess of +5.5 V.