CiA 402: Drive Profile and State Machine
What is CiA 402?
CiA 402 is the standardized drive profile for servo, frequency converter, and stepper motor drives in accordance with IEC 61800-7-201. It defines a uniform finite state machine, standardized operating modes, and a common object dictionary—independent of the manufacturer and the fieldbus used (CANopen, EtherCAT CoE, POWERLINK).
Why is this important?
Without a standardized drive profile, each drive would have to be controlled using manufacturer-specific commands, states, and parameters. CiA 402 creates a common language:
- Cross-manufacturer control — an EtherCAT master can control drives from different manufacturers using the same commands
- Standardized commissioning — Engineers learn a state machine that functions identically for all CiA-402-compliant drives.
- Reduced integration effort — standardized PDO mappings, error codes, and behaviors shorten development time
- Future-proof — the standard is maintained by CAN in Automation (CiA) and is anchored in the IEC 61800 family of standards.
How does it work?
The state machine (8 states, 16 transitions):
The core of CiA 402 is a state machine that controls the operating state of the drive. The motor can only be moved when it is in the "Operation Enabled" state. The most important states are:
- Switch On Disabled — Drive initialized, power stage disabled
- Ready To Switch On — Ready to activate the power level
- Switched On — Power stage active, but motor control not yet enabled
- Operation Enabled — Full control active, motor can be moved
- Quick Stop Active — Controlled rapid braking in progress
- Fault — Error occurred, drive locked; can only be reset by Fault Reset
Control word and status word:
Control is performed via two 16-bit words: The control word (0x6040) is written by the master and triggers state transitions. The status word (0x6041) is reported back by the drive and shows the current status, warnings, and operating mode-specific information.
Operating modes (0x6060):
CiA 402 defines standardized operating modes for each control variable:
- Profile modes (PP=1, PV=3, PT=4) — the drive generates the trajectory internally; the master specifies target values and profile parameters
- Cyclic synchronous modes (CSP=8, CSV=9, CST=10) — the master sends setpoints in each communication cycle; preferred for robotics and multi-axis systems
- Homing (HM=6) — Reference run to determine the absolute position
The typical start sequence: Shutdown (0x0006) → Switch On (0x0007) → Enable Operation (0x000F).
How does SOMANET implement this?
All SOMANET servo drives (Node and Circulo) implement CiA 402 via EtherCAT (CoE) and support all six main operating modes: PP, PV, PT, CSP, CSV, and CST. The cyclic synchronous modes are optimized for robotics applications, while the profile modes are optimized for point-to-point applications.
The internal sampling cycle is 250 µs, and the recommended master cycle time is between 250 µs and 8 ms. Distributed clocks synchronize multi-axis systems. Manufacturer-specific extensions (commutation, encoder configuration, protective functions) are stored in the 0x2000–0x5FFF range.
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