Beckhoff BK1120/BK1250 EtherCAT Coupling Debugging and KL Terminal Parameterization Complete Guide

Beckhoff BK1120/BK1250 EtherCAT Coupling Debugging and KL Terminal Parameterization Complete Guide

Introduction: The Bridge between EtherCAT and K-bus

In Beckhoff's I/O system, the bus coupler is a key component for converting fieldbus protocols to internal terminal buses (K-bus or E-bus). For a large number of users who are still using the classic KL series bus terminals, BK1120, BK1150, and BK1250 provide a solution that combines EtherCAT high-performance networks with mature and stable K-bus terminals.

BK1120/BK1150: As EtherCAT slave stations, directly connect to the EtherCAT network and connect to KL series terminals (K-bus).

BK1250: Its special feature lies in its "terminal type" housing, which can be hung behind the E-bus (EL terminal) to achieve the conversion from E-bus to K-bus, thus mixing EL and KL terminals in the same terminal block.

These three couplers all support up to 64 KL terminals (up to 255 through K-bus extension), with a maximum process data input/output of 1024 bytes. They inherit all the advantages of the Beckhoff bus terminal system: automatic terminal recognition, flexible configuration, and high reliability diagnosis. This article is based on the official manual and systematically outlines the installation, parameterization (especially the register communication of KL terminal), diagnosis, and troubleshooting process of BK couplers, providing a practical guide for on-site engineers.

Mechanical installation and power wiring

2.1 Installation on DIN rail

BK1120 (width 49mm) and BK1150/BK1250 (width 15mm) are both installed on 35mm DIN rails (EN 60715). When installing, first hang the coupler on the upper edge of the guide rail and press down until the lock buckle clicks into place. When disassembling, use the orange release handle (or a screwdriver to pry the locking hook) to remove it. Requirements for enhancing mechanical load capacity: Use TH35-15 guide rails, install fixing components at both ends of the terminal block, with a distance of 5cm between the fixing points of the guide rails, and a total length of no more than 64 12mm terminals or 32 24mm terminals.

2.2 Power Supply and Grounding

The coupler requires 24V DC (-15%/+20%) power supply and is connected through the top spring terminal

Us (terminals 1 and 5): supplies power to the electronic part of the coupler and K-bus (maximum 1750mA for K-bus).

Up (terminals 2/6 and 3/7): Provides power to the power contacts for on-site power supply of peripheral devices (such as sensors), with a maximum current of 10A (requires 10A slow melting fuse).

PE (terminal 4/8): protective grounding, must be at a common potential with 0V and comply with PELV requirements.

Important isolation: There are three potential groups inside the coupler: EtherCAT side, K-bus electronic side, and power contact side, which are electrically isolated from each other (500V). PE contacts shall not be used for other potentials, and there is capacitive coupling between PE and the installation guide rail. The PE feeder shall be disconnected during insulation testing.

2.3 EtherCAT Network Wiring

Use standard CAT5e shielded Ethernet cables (such as Beckhoff ZB9010/9020), RJ45 connectors, and pins that comply with Ethernet standards (1/2 transmit, 3/6 receive). The coupler has automatic crossover function and supports direct or crossover lines. Two RJ45 interfaces (X1 IN/X2 OUT) are used for cascading, and the cable length between any two devices is ≤ 100m.

Startup behavior and distributed clock (DC)

After the coupler is powered on, it first performs a self check (red I/O ERR LED flashing), then scans the connected KL terminal to establish an internal structure list. If there are no errors, the I/O ERR LED will turn off and the coupler will enter the EtherCAT state machine process (Initiat → PREOP → SAFEOP → OP). If the terminal configuration is incorrect, the coupler will remain in the STOP state.

Regarding distributed clocks: BK1150 supports as a DC reference clock starting from revision number -0016 and firmware 01. To use it as a reference clock, check "Cyclic Mode Enable" and "Use as potential Reference Clock" in the "Advanced Settings" of TwinCAT. Infrastructure components such as system couplers are not used as DC references by default, but can be activated as needed.

Three ways to parameterize KL terminals (register communication)

Many parameters of KL series terminals (especially analog and special function terminals), such as range, filtering, user scaling, and bias, are managed through internal "registers". The BK coupler, as a gateway, provides the following three register access methods:

4.1 Approach 1: CoE Startup List - Recommended for Permanent Parameterization

This method automatically writes parameters to the specified KL terminal every time the system starts, even if the terminal is replaced, the parameters can be restored. Core steps:

In TwinCAT, select the "Startup" tab of the BK coupler.

Insert an entry in the PREOP → SAFEOP conversion:

Firstly, write 0x427F:00 as the target terminal number (the first KL terminal number is 1).