Operation
41
4
shows the internal block diagram of Atlas. Here are summary descriptions of the major modules and
functional areas:
Commutation
—this module utilizes internally generated information, or information provided by the external
controller, to split up the desired overall torque command into individual phase commands to drive Brushless DC and
step motors.
Current Loop
—this module inputs the desired current for each motor coil and uses the measured current feedback
from each motor coil to develop PWM (pulse width modulation) output command values for the power stage.The
current loop module may be disabled, in which case Atlas will drive the motor in voltage mode. See
for more information on the current loop module.
Power Stage
—this module receives desired voltages for each motor coil and manages the Atlas unit’s high
performance MOSFET-based switching bridge to precisely drive the coils of the motor. See
for a detailed description of this module.
Status Registers
—this module holds various status registers including an Event Status Register, a Drive Status
register, a Drive Fault Status Register, a signal status, and an SPI Status Register.
Safety Processing
—this module manages Atlas unit safety-related functions including the internal temperature
sensor, bus voltage error, the
Enable
input signal, current foldback, the
FaultOut
output signal, event action processing,
and more.
Step Motor Processing
—this module implements step motor-specific features including microstep signal
generation, holding current management, and
Pulse
,
Direction
, and
AtRest
signal processing.
Memory Buffers
—this module provides user-accessible memory for trace and setup parameter configuration storage.
Trace
—this module provides a facility for continuously storing up to four simultaneous Atlas variables in the memory
buffers.
Power-up & Non-Volatile Initialization Storage
—this modules manages the power-up sequence and provides the
ability to store selected parameter into the Atlas unit’s non-volatile memory.
SPI Command Processor
—This module, described in the next chapter, manages all communications to/from the
external controller.
4.3
Notes on Command Mnemonics
For simplicity, throughout this and subsequent chapters, we will use a mnemonic-style nomenclature to indicate
external controller commands sent to Atlas. Such commands are sent over an SPI (serial peripheral interface)
connection, using a packet-based protocol designed to control all aspects of Atlas unit’s operation. Atlas supports over
65 commands through this powerful and flexible protocol.
For example, to set the proportional current gain, the command:
SetCurrentLoop
is used.
The actual data packet sent to Atlas to effect the
SetCurrentLoop
command is a specific sequence of signal states on
the SPI data lines, not the mnemonic itself. However to more easily illustrate command sequences, the mnemonic
format will be used throughout this manual.
See
Chapter 5, “SPI Communications”
for complete command details, along with other aspects of the SPI protocol.
Atlas
®
Digital Amplifier Complete Technical Reference
