PMD Atlas Compact, Complete Technical Reference

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Operation
Atlas® Digital Amplifier Complete Technical Reference
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Overall, Atlas provides two step-motor specific position command methods. These are summarized in the table below:
4.9.1 Pulse & Direction Signal Input Mode
Figure 4-11:
Pulse and
Direction Signal
Input Mode
Control Flow
Figure 4-11 shows the control flow of the Atlas when used in pulse & direction signal input mode. The Atlas
Pulse
signal drives a counter which increments or decrements a step motor command position based on the state of the
Direction
signal. Pulse signals are expected to be active low, meaning that a position increment or decrement occurs
when this signal transitions from high to low. The Direction signal indicates that a pulse received while the Direction signal
is low is interpreted as a negative direction command, and a pulse received while this signal is high as a positive
direction command.
Atlas provides programmable microstepping resolution, which means that the incoming position data stream can be
interpreted by the Atlas at various resolutions. The maximum is 256 microsteps per full step, and the default
interpretation is 64 microsteps per full step. This means that in the default condition, for a standard 1.8
° two-phase
stepper, Atlas provides a resolution of 12,800 microsteps per mechanical motor rotation, or roughly .028 degrees of
mechanical motion per incoming pulse. Note that the control resolution may not equal the actual system accuracy.
To set the microstep resolution the command SetPhaseCounts is used. To read this value back, the command
GetPhaseCounts
is used. Phase counts are expressed as microsteps per electrical cycles and there are four full steps
per electrical cycle. So for example, to set 256 microsteps per full step, the command SetPhaseCounts 1,024 is used.
Position Command Mode Description
Pulse & direction signal input Atlas directly supports input of hardware Pulse , Direction , and AtRest sig-
nals to interface with traditional external controllers that provide these
signals. When operated in this mode, SPI communication is not available.
SPI pulse & direction This pulse & direction interface utilizes the external controller SPI inter-
face to provide continuous position information to Atlas. Compared to
pulse & direction signal input, this approach allows full use of the SPI
communication interface.
When actually connected to Atlas in pulse & direction signal mode, SPI communication is not available. Command
examples in this section are therefore provided for use during setup, before pulse & direction signal mode is op-
erational.
Holding Current
Pulse
Direction
Drive Current
Position
Counter
Microstep
signal
generation
To
current
loop or
power
stage
Phase A
Command
Phase B
Command
AtRest Asserted?
Y
N