Operation
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Atlas® Digital Amplifier Complete Technical Reference
4
4.9.1.1
Setting the Motor Current
When operating in pulse & direction input mode the current output by Atlas must be specified. Atlas supports two
separate, programmable torques. The first is called the drive current and is used during normal step motor operations.
The second is called the holding current and is used when the motor is stationary as indicated by the
AtRest
signal. This
signal is typically set when the external controller’s trajectory generator completes its move or shortly thereafter.
AtRest
is an active low signal, meaning when no motion is occurring this signal should be is set low, and set high when motion
is occurring.
To set both the drive current and the holding current the command
SetCurrent
is used. A value between 0 and 32,767
is set. The scaling of this command is determined by the particular Atlas you are using. See
for details. To read this value, the command
GetCurrent
is used.
4.9.1.2
Pulse & Direction Signal Mode Operation Setup
Because Atlas shares SPI bus signal pins with the
Pulse
,
Direction
, and
AtRest
pins it is not possible to operate the Atlas
in the pulse & direction signal input mode while communicating via the SPI communication bus.
To resolve this, Atlas is first connected in SPI mode, and the SPI interface is used to optimize the motion control
application during application development and to download desired drive parameters to Atlas unit’s non-volatile
initialization storage memory. See
for more information on non-volatile initialization
storage.
Once Atlas has been fully prepared, to switch Atlas to pulse & direction signal input mode the command
SetDriveCommandMode
is used. This command takes effect immediately, so further SPI command processing is
disabled, and the external controller should begin sending pulse & direction commands. Note that this command
sequence is generally only performed during power-on initialization. See
for more
information.
4.9.1.3
Recovering from Pulse & Direction Signal Mode
It is possible to restore an Atlas that is functioning in pulse & direction signal mode to SPI operation. While this is an
uncommon operation, it may be useful for testing, diagnosing a field problem, or to allow a production Atlas to be
used for prototyping with optimization software such as PMD’s Pro-Motion software. Here is how such a recovery is
accomplished.
For approximately 250 ms after power on Atlas will monitor its
Pulse
and
Direction
input signals for a special pattern.
If detected, this recovery pattern will cause the Atlas to revert to SPI communication mode.
The recovery pattern consists of a rising edge on the
Pulse
signal with the
Direction
signal set low, five pulses (ten edges)
on the
Direction
signal, followed by a falling edge on the
Pulse
signal. The time between direction edges is required to
be at least 500 us, and the
AtRest/~SPICS
signal should be low throughout the recovery pattern.
Note that in this recovery pattern
Direction
signal edges occur while the
Pulse
input signal is high, contrary to normal
pulse and direction input where a step is signaled by a high to low transition of the
Pulse
input, and all
Direction
edges
should occur while
Pulse
is low. Note also that when in pulse and direction signal input mode the
SPISO
pin is in a high
impedance state. Once the recovery pattern is recognized
SPISO
is driven low.
Once the command mode has been set to pulse and direction signal, Atlas will be in pulse & direction signal mode
and the SPI bus will no longer be functional until a subsequent power cycle occurs.
