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5.3.3 Stepped input command
The stepped inputs may be configured as quadrature or step and direction interfaces. For each
forwards or backwards step received, the commanded position moves by a configurable step in
the relevant direction.
For quadrature mode, input A leads input B when commanding forwards movement on the
stage; and input B leads input A when commanding backwards movement. With the standard
Gray Code system as used for stepper motor controllers, each edge on each input indicates a
step in the appropriate direction.
For step and direction mode, input B controls whether a step is to be forwards or backwards,
and a rising edge on input A triggers a step in the appropriate direction.
To ensure the controller can be easily integrated with other systems, this is also configurable to
reverse direction, and for step and direction mode to trigger on rising or falling edge.
5.3.4
Function playback
Function playback allows a waveform to be set up by the PC and triggered to play without
further intervention from the PC. Digital commands cannot be sent to the controller as fast as
the controller’s sample rate, so this allows the playback of more accurate movement profiles, as
well as ensuring the waveform does not suffer from the inevitable jitter associated with sending
periodic digital commands over a communications interface.
Configurable trigger outputs allow external equipment such as a camera to be triggered
synchronously with the waveform, for example at intervals during a constant-velocity ramp.
Configurable trigger inputs may be used to start, stop or pause playback on any channels, after
waveforms have been set up by the controlling PC, allowing integration with control hardware.
5.4
POSMON output
5.4.1
Analogue POSMON
The NPC-D-6xx0 generates an analogue output proportional to the stage position relative to its
nominal position for each channel. This is called Position Monitor or POSMON. It is a single ended
analogue output with the connector shell connected to ground.
Input A
Input B
Forwards steps
Backwards steps
Quadrature mode
Forwards steps
Backwards steps
Step and direction mode
Figure 3: Stepped input commands
