National Instruments FW-7344, Hardware User Manual

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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.