Investigating EtherCAT Communication Errors with EC-Engineer

Introduction

Common Causes of EtherCAT Communication Errors

EtherCAT networks are often large and physically distributed. A single system may include hundreds of SubDevices, long cable runs, and connectors exposed to vibration, EMI, and temperature changes.
When communication issues arise, the symptoms are usually generic:

• the network does not get to OPERATIONAL (OP) state,
• one or more SubDevices are missing,
• CRC counters increase,
• frames are lost,
• or SubDevices unexpectedly leave OP state.

The challenge is that the root cause is often localized, even though the impact is global. A single damaged cable or marginal connector can destabilize the entire network. Without proper diagnostics, finding that one weak link can be time-consuming, frustrating, and costly.
EtherCAT provides extensive built-in diagnostic information. EC-Engineer makes that information visible and useful.

How EtherCAT Detects and Localizes Errors

EtherCAT provides built-in diagnostic mechanisms that make it possible to detect communication errors and narrow them down to a specific device, port, or network segment. EC-Engineer exposes these mechanisms in a structured, graphical way, allowing engineers to move from symptom to root cause efficiently.

Frame Loss and CRC Errors

One of the most common indicators of EtherCAT communication problems is frame loss or frame corruption. Each EtherCAT SubDevice checks passing frames for integrity using CRC calculations. When corrupted frames are detected, error counters are incremented at the SubDevice level.

When the frame returns to the MainDevice, the Ethernet controller performs its own CRC validation. If the frame is invalid, it is discarded. EC-Engineer makes these CRC and receive error counters visible through its Hardware Diagnostics and Topology View, allowing engineers to identify whether errors originate from a specific SubDevice, port, or cable path.

This mechanism is especially effective for localizing physical-layer issues such as damaged cables, poor connectors, and electromagnetic interference.

Working Counter (WKC)

The Working Counter is a core EtherCAT mechanism used to verify successful communication across the entire network. Each EtherCAT datagram defines an expected Working Counter value based on the command type and the number of addressed SubDevices.
As a frame passes through the network, every SubDevice that processes the datagram increments the counter. When the frame returns to the MainDevice, the received Working Counter is compared to the expected value. If the values do not match, at least one SubDevice did not process the datagram correctly.
EC-Engineer displays Working Counter consistency as part of its diagnostic information, helping engineers quickly determine whether a communication issue affects a single device or the entire network. This information is often used together with Topology View and Self-Test Scan, which are discussed later in this article.

Hardware vs. Software Diagnostics

EtherCAT diagnostics can be divided into two complementary categories: hardware diagnostics and software diagnostics.
Hardware diagnostics focus on the physical communication path. These include link status, CRC counters, receive error counters, and network topology integrity. In EC-Engineer, this information is available through Hardware Diagnostics and visual indicators in the Topology View, making it easier to spot failing ports, cables, or connections.
Software diagnostics focus on protocol and application-level behavior. These include AL status codes, SubDevice state machine transitions, startup configuration errors, watchdog events, and Distributed Clocks synchronization issues. EC-Engineer presents this information through the General tab and Messages window, providing context for why a SubDevice may fail to reach or remain in OP state.
By combining hardware and software diagnostics in a single interface, EC-Engineer enables faster root-cause analysis without requiring low-level packet tracing or protocol decoding.

EC-Engineer as a Diagnostic Platform

EC-Engineer is designed as a single, powerful tool for EtherCAT configuration, diagnosis, and monitoring. It can be used during all phases of an EtherCAT project, from initial network design and configuration to troubleshooting, maintenance, and system validation. As a diagnostic platform, EC-Engineer offers many helpful features that take advantage of EtherCAT’s native error handling mechanisms.

At the platform level, EC-Engineer provides the following capabilities:

• Support for EC-Master and many third-party MainDevices
• Graphical visualization of network topology
• Integrated message and log window
• Live monitoring of process data
• Snapshot and offline diagnosis for documentation and analysis
• Remote access to EC-Master via RAS (Remote Access Server)

Key EC-Engineer Features for Investigating Communication Errors

Self-Test Scan

Self-Test Scan performs an automated, in-depth analysis of the EtherCAT network. It sends a large number of diagnostic frames and evaluates lost frames and SubDevice error counters. This makes it possible to detect and localize unstable connections and faulty components that may not fail consistently.

Topology View

EC-Engineer’s Topology View provides a graphical representation of the EtherCAT network, including port-level status indicators. Missing devices, crossed connections, and degraded links can often be identified and located immediately.

Hardware Diagnostics

Hardware Diagnostics expose detailed information such as CRC counters, receive errors, and link status. These indicators are essential when troubleshooting physical-layer issues.

Network Mismatch Analyzer

EC-Engineer’s Network Mismatch Analyzer compares the pre-configured ENI file with the actual network. It helps identify missing SubDevices, unexpected devices, or configuration discrepancies that prevent the network from starting correctly.

Rescue Scan

Rescue Scan can be used when the network cannot be fully initialized. It isolates faulty connections and restores communication with reachable SubDevices, allowing partial operation and faster recovery.

Live Monitoring of Process Data

Live monitoring allows engineers to inspect process data, including position and velocity values, drive status and control word, digital and analog I/O states, and application-specific status flags. These values help confirm that process data is being updated cyclically and consistently across the network. Stale values, unexpected jumps, or delayed updates can indicate communication issues even when the network appears operational.

Snapshot and Offline Diagnosis

Snapshots capture the complete network state, including detected errors and counters from a diagnostics session, at a specific moment. These snapshots, which can be saved as one or multiple snapshots, can be analyzed later or shared with colleagues or technical experts, making them useful for intermittent faults and documentation.

Deep-Dive: Using Self-Test Scan to Detect Communication Errors

Self-Test Scan is one of the most effective tools in EC-Engineer for identifying and localizing EtherCAT communication errors. It is specifically designed to uncover issues that are difficult to detect during normal operation, such as intermittent frame loss or marginal physical connections.

How Self-Test Scan Works

The underlying principle of Self-Test Scan is to actively stress the EtherCAT network under controlled conditions. During the scan, a large number of EtherCAT frames of varying lengths are sent over a defined period of time and monitors whether all frames sent by the MainDevice are successfully received again.

Frames that are lost on their path through the network or marked as corrupted by SubDevices are counted continuously. In parallel, the Ethernet controller in the MainDevice verifies frame integrity using CRC calculations and discards invalid frames. At the end of the test run, EC-Engineer reads the error registers of all SubDevices and evaluates the collected data.

The results are automatically processed and presented to the user in EC-Engineer, eliminating the need for manual interpretation of raw counters.

What Data Self-Test Scan Provides

Self-Test Scan consolidates multiple diagnostic indicators into a single, easy-to-interpret view. The results include lost-frame statistics, error counters, and detailed information about which SubDevices or ports exhibit abnormal behavior.

Detected issues are visualized directly in the graphical topology view, where affected SubDevices or EtherCAT ports are highlighted in an easy-to-read color-coded manner. Additional information is available at the network level, including error counters, lost frames, and diagnostic messages. For deeper insight, port-level and device-specific details of individual SubDevices can be accessed through the “Extended Diagnostics” tab, as shown in the screenshot below.

This combination of visual indicators and detailed counters allows engineers to localize the source of communication problems quickly, even in large networks with many SubDevices.

Practical Examples

Self-Test Scan is particularly valuable in networks with many cables, connectors, and junctions, where a single weak connection can destabilize the entire system. In practice, it is commonly used to identify intermittent CRC bursts caused by faulty cables or connectors, isolate a single failing component in an otherwise healthy network, and verify the integrity of newly installed EtherCAT networks.

Because Self-Test Scan can fully load the EtherCAT bus up to 100 percent utilization, it is also well-suited for preventive testing. Networks that appear stable during normal operation can be stressed deliberately to uncover potential problem areas before they lead to failures in the field. This makes Self-Test Scan a powerful tool not only for troubleshooting, but also for commissioning, validation, and long-term reliability assurance.

Importantly, these capabilities are directly usable in EC-Engineer without requiring deep EtherCAT expertise or prior training. Errors and weak points are presented in a clear and understandable way, allowing issues to be identified and addressed faster, especially in situations where system downtime must be minimized.

Using EC-Engineer with acontis’ EC-Master vs. Third-Party MainDevices

MainDevice-Independent Diagnostics

Many of EC-Engineer’s diagnostic functions are available regardless of the MainDevice vendor. These include the topology view, error counters, CRC monitoring, and state machine monitoring. EC-Engineer can be used to scan the network to find EtherCAT devices or a valid ENI file can be imported into EC-Engineer to build the expected network.

Additional Insights with acontis' EC-Master

When EC-Engineer connects to a network using EC-Master as the MainDevice via RAS, additional diagnostic information becomes available. This includes deeper visibility into the MainDevice state and synchronization behavior.

Best Practices to Prevent Recurring Communication Errors

Many EtherCAT communication issues are not caused by software defects, but by physical, environmental, or configuration-related factors that develop over time. Applying a small set of proven best practices during design, commissioning, and maintenance can significantly reduce the likelihood of recurring communication errors. These measures also make it easier to detect potential issues early, before they impact system operation.

• Use conformance-tested hardware
• Ensure proper grounding and shielding
• Avoid low-quality cables and connectors
• Monitor CRC counters regularly
• Run Self-Test Scan during development
• Implement RAS in EC-Master applications to enable remote diagnostics

Other Available Software Tools and When to Use Them

While EC-Engineer handles most EtherCAT configuration and troubleshooting tasks, certain diagnostic scenarios may require additional tools. acontis offers complementary software solutions that enhance EtherCAT insight, especially for custom long-term monitoring, quick health checks, and MainDevice-independent traffic analysis.

• EC-Lyser: lightweight diagnostic tool for use with EC-Master, well-suited for quick health checks and maintenance tasks, and when configuration changes are not required.
• EC-Monitor: Software library with a C/C++ API for customized, long-term, MainDevice-independent EtherCAT monitoring. This solution requires a TAP.
• EC-Inspector: MainDevice-independent EtherCAT monitoring and analysis via a TAP, intended for detailed traffic inspection.