Application Notes
176
Atlas® Digital Amplifier Complete Technical Reference
B
B.5
Step Motor Atlas with ARM
Microcontroller
The following schematic shows a step motor Atlas amplifier connected to an STMicroelectronic’s ARM
microcontroller. Atlas receives torque commands through the ARM's SPI interface.
A wide variety of microcontrollers, DSP-type devices, or FPGAs supporting SPI interfaces can control Atlas directly.
STMicroelectronic’s STR912FAZ44H6T is used in this example. Users design their own motion control algorithms
on the microcontroller, which in turn commands Atlas to drive the motor.
B.5.1
Atlas Power Input and Motor Outputs
Atlas is powered through pin pairs HV and Pwr_Gnd, and the power source is a transformer-isolated DC power
supply.
For step motors pins MotorA, MotorB, MotorC and MotorD are wired to motor windings A+, A-, B+ and B-,
respectively.
Please refer to B.1 for layout and wiring recommendations on power input and motor outputs.
B.5.2
Atlas SPI Interface
Atlas functions as an SPI slave, receiving control commands from the ARM through its SPI interface. Atlas SPI
communication is enabled when ~SPICS is pulled down.
Please refer to B.1 for layout recommendation on SPI interface.
B.5.3
Atlas ~Enable and FaultOut Signals
Atlas has one dedicated input signal, ~Enable, which must be pulled low for the Atlas output stage to be active.
FaultOut is a dedicated output. During normal operation it outputs low. When a fault occurs it will go into a high
impedance state. In this example, FaultOut is pulled up by Vpullup through resistor R1. Vpullup can be up to 24V to
meet the system requirement. For example, if the fault signal is wired to a 5V TTL input, Vpullup can be 5V.
B.5.4
Microcontroller Configuration
In this schematic, the host controller is ST’s STR912FAZ44H6T. The microcontroller’s SPI port is used for SPI
communication.
In this example output pin K7 of the U1 (ARM processor) is used to control Atlas' ~SPICS input. ~SPICS has an
internal pull-up, therefore, during power up and after reset, the control pin should be in high-impedance or output
high state to disable the SPI.
