Glossary Updates12 new terms added to the glossaries · October 2, 2026, 22:44 CEST
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Glossary · Industrial communication

EtherCAT state machine

Also known as: ESM, EtherCAT device state machine

German: EtherCAT-Zustandsmaschine

In EtherCAT, the EtherCAT state machine is the communication state model of every subdevice, controlled by the main device, with the states Init, Pre-Operational, Safe-Operational and Operational, plus the optional Bootstrap state for firmware updates.

  • Industrial communication
  • Standards

In one sentence

The EtherCAT state machine moves each subdevice through Init, Pre-Operational, Safe-Operational and Operational, plus Bootstrap for firmware.

Example

After power-up, a filler's EtherCAT drives stay in Safe-Operational, sending inputs but holding outputs in a safe state, until the controller has checked their configuration and requests Operational.

How it applies

  • Engineering: Each state enables more communication: Init none, Pre-Operational mailbox communication (for example parameter access via CANopen over EtherCAT (CoE)), Safe-Operational cyclic inputs with outputs held in a safe state, Operational inputs and outputs. The main device checks the configuration on each transition.
  • Commissioning: A device that refuses a transition reports an AL status code, for example for an invalid process data mapping or a missing sync signal. These codes are the first thing to read when a device "hangs" in Pre-Operational or Safe-Operational.
  • Maintenance: Firmware is loaded in Bootstrap, typically with File access over EtherCAT (FoE), and only on devices that support it.
  • Documentation: The documentation team documents the device-specific behavior in each state, the meaning of the AL status codes and LED patterns, and what the machine does when a device drops out of Operational. The communication state is not a Safe state of the machine; that is defined by the safety functions.

EtherCAT state machine vs. machine state model

The EtherCAT state machine describes the communication of one device. Machine operating states, such as those in PackML (ISA-TR88.00.02), describe the behavior of the whole machine and are programmed in the controller.

By knowledge.aitechdoc.world · Published September 28, 2026 · Last reviewed

Source: IEC 61158 (Type 12) and IEC 61784-2 (communication profile family 12), and EtherCAT Technology Group publications

Definitions follow the cited standards and specifications. Where a source is a copyrighted publication, such as an ISO, IEC or EN standard, the definition is a close paraphrase, not a verbatim quotation, so as not to infringe copyright. We recommend reading the original publication. The sections “How it applies” are editorial commentary by AI TechDoc Knowledge and are not part of any standard.

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