Beckhoff EL Series EtherCAT Terminal Compatibility

Compatibility Overview

Beckhoff EL Series EtherCAT Terminals represent a high-performance slice-based I/O architecture running on the EtherCAT protocol. Unlike legacy Beckhoff KL Series terminals, which utilize the proprietary, transmission-heavy K-bus (a parallel local terminal bus), EL Series terminals communicate via the E-bus. The E-bus physical layer is an extension of the EtherCAT protocol based on Low Voltage Differential Signaling (LVDS). Standard EtherCAT packets (100BASE-TX) entering through an EK1100 or EK1101 bus coupler are processed directly by each terminal's ASIC (EtherCAT Slave Controller, or ESC) in real time.

Integrating these terminals within an industrial network requires a detailed understanding of physical backplane constraints, protocol bridging, power budgets, and firmware synchronization. When deploying EL components, physical slot placement must match the logical channel sequence, and the total current draw from the E-bus must be calculated to prevent bus failure.

Supported Models

The EL Series offers wide-ranging support across digital, analog, safety, and specialized physical interfaces. Each terminal must connect to an active EtherCAT Coupler to interface with the main fieldbus line. The table below outlines common supported models, their functional categorization, hardware specifications, and compatibility variables:

All supported EL units require an EtherCAT Slave Information (ESI) XML configuration file mapped to the designated TwinCAT system manager or third-party EtherCAT master configuration environment.

Unsupported Models

Because the physical envelope of Beckhoff EL Series terminals is identical to the KL Series (K-bus) terminals, compatibility errors can occur during legacy system upgrades.

1. K-bus Terminals (KL Series): Modules such as the KL1104, KL2134, or KL3002 utilize the K-bus backplane protocol rather than the E-bus framework. They cannot be placed onto standard EK1100 bus coupler setups. Placing a KL terminal directly between EL terminals breaks the continuity of the EtherCAT physical loop, terminating communication for all downstream terminals.
2. Legacy Fieldbus Couplers: Legacy master modules (such as the BK3120 for PROFIBUS or BK9000 for Modbus TCP) cannot read or host EL series E-bus modules.
3. Third-Party Masters Lacking EtherCAT ESI Integration: EtherCAT masters that do not fully support dynamic configuration of objects or matching ESI XML schemas will fail to configure specialized EL units like the EL5101 (Encoder Interface) or EL7041 (Stepper Motor Interface).

Communication Options

EL Series terminals can interact directly with diverse industrial communications architectures. Through specialized gateway terminals inserted directly into the E-bus terminal group, users can extend local Beckhoff I/O racks to foreign network infrastructures:

• EtherNet/IP: Using the EL6652 terminal, the EtherCAT cluster can interface as an adapter or scanner on an EtherNet/IP network. This facilitates native CIP (Common Industrial Protocol) message routing to Rockwell Automation Logix controllers.
• PROFINET RT: The EL6631 terminal enables integration with Siemens S7-1200 or S7-1500 controllers via PROFINET RT. It handles cyclic data exchange and acyclic alarms over the PROFINET layer.
• Modbus TCP & RTU: Modbus RTU communication can be achieved locally through serial terminal slices (such as the EL6002 or EL6022 dual-channel interfaces) operating RS232, RS422, or RS485 standards.
• CC-Link / CC-Link IE Field: The EL6720 CC-Link terminal acts as a transmitter-receiver, enabling reliable connectivity to Mitsubishi and other CC-Link partner networks.

Integration Notes

To ensure flawless integration of EL Series terminals, engineers must adhere to several operational criteria:

1. E-Bus Power Calculation: The EK1100 coupler feeds 5V DC directly to the E-bus to power the internal logic of the EL slices. The coupler provides up to 2A (2000 mA). Each terminal draws varying current (e.g., EL1008 draws 90 mA; EL5101 draws 130 mA). If the total calculated current of the terminal configuration exceeds 2A, you must insert an EL9410 or EL9400 power supply terminal to refresh the backplane logic power. Failure to do so will result in cyclic drops, unexpected bus resets, and intermittent frame loss.
2. ESI XML Files Integration: When configuring third-party controllers (e.g., Omron Sysmac, CODESYS, or VIPA PLC), matching ESI files must be imported into the configuration tool. Pay special attention to the Revision Suffix (e.g., -0018 vs -0000). Select the target revision that matches or precedes the revision stamped on the terminal tag.
3. TwinCAT System Manager Setup: When initializing the system, scan the I/O in TwinCAT Config Mode. This allows the system to auto-detect and construct the physical physical topological map, helping prevent manual configuration entry mistakes.

Common Compatibility Issues

• TwinCAT Error Code 0x0012 (Invalid SM Settings / Revision Mismatch): This occurs when the downloaded hardware configuration contains a newer XML revision of an EL series terminal than what is physically installed. Revert the offline hardware model to the exact revision number stamped on the physical terminal housing.
• State Machine Stuck in Safe-Operational (Safe-Op): This typically indicates that although the master has initialized cyclic communication, the process data limits (PDOs) do not match the expected state, or the distributed clock synchronization failed. Check if Distributed Clocks (DC) are enabled on a terminal operating behind an EtherCAT master that does not support active DC synchronization.
• Physical Interlocking of K-Bus and E-Bus Terminals: Although both terminal families slide onto standard 35mm DIN rail and locking tabs fit together, doing so without a transition terminal (such as an EL9011 or specialized BK/EK bridge) corrupts the backplane pin assembly, leading to a physical system halt.

FAQ

Q: Can I mix KL and EL terminals on the same DIN rail?

A: Yes, but only with a specialized coupler or bridging configuration. You cannot plug K-bus (KL) terminals directly onto an E-bus (EK1100) coupler segment. To merge both systems, you must either use a BK1120 coupler for the K-bus slices or end the E-bus segment with an EL9011 and bridge protocols via a system controller.

Q: What is the significance of the revision number on the EL terminal label?

A: The revision number (e.g., EL1008-0000-0018) denotes the hardware step and matching ESI XML file required by the programming tool. While higher physical revisions have backward compatibility with older configurations on the physical level, configuring a newer hardware profile in software without installing the matching physical card will prevent OP mode.

Q: How do I resolve a state machine initialization failure with code 0x0014 (Safe-Op to Op failed)?

A: This points to process data configuration failures. Verify that the correct PDO mapping is chosen in the "Process Data" tab of TwinCAT or your equivalent master IDE. Ensure that any auxiliary power terminals (like EL9410) are injecting the necessary field power to digital input or output circuits.

Q: Can EL Series terminals run under an standard Ethernet switch?

A: No, standard managed or unmanaged Ethernet switches cannot handle the specialized ring-delay topology of native EtherCAT E-bus frames unless you utilize specialized EtherCAT media converters (such as target ET9000 or EK1122 units). Standard IT switches will drop custom real-time EtherCAT frames.

Q: Are Beckhoff EL terminals compatible with non-Beckhoff controllers?

A: Yes, they are compatible with any standard EtherCAT Compliant Master (such as Omron NJ/NX series, B&R controllers, or CODESYS runtime devices) provided the master tool imports the correct ESI XML configuration files provided by Beckhoff.