BECKHOFF EL600x/EL602x Serial Port Module Debugging Manual

BECKHOFF EL600x/EL602x Serial Communication Module Debugging, Maintenance, and Troubleshooting Guide

In industrial automation sites, serial communication remains an important way to connect devices such as sensors, barcode scanners, GPS clocks, and frequency converters. The Beckhoff EL600x (RS232) and EL602x (RS422/RS485) series EtherCAT serial port terminal modules are an ideal choice for serial device integration in EtherCAT systems due to their flexible baud rate configuration, 864 byte receive buffer, and optional transmission rate optimization function. However, when faced with practical issues such as setting RS485 bus terminal resistance, switching between half duplex/full duplex modes, TwinCAT process data mapping, and firmware version compatibility, engineers often need a systematic practical guide. This article is based on official technical documentation and presents a comprehensive professional manual covering model identification, installation and wiring, CoE parameterization, process data configuration, firmware updates, and fault diagnosis.

Product Series Overview and Selection Core

The EL600x/EL602x series includes single channel and dual channel versions, covering mainstream serial interface standards:

Model Interface Type Channel Number Key Characteristics

EL6001 RS232C 1 full duplex, RTS/CTS hardware handshake, up to 15m in length

EL6021 RS422/RS485 1 Full/Half Duplex, Differential Signal, Maximum 1000m

EL6021-0021 RS422/RS485 1 Increase bias resistance, suitable for connecting in the middle of the bus

EL6002 RS232C 2 dual channels, each channel with a DE9 male head

EL6022 RS422/RS485 dual channel, DE9 female head, each channel can output 5V/20mA power supply

All models have a default baud rate of 9600, 8 data bits, 1 stop bit, and no checksum (8N1). Key selection decision: If long-distance (>15m) or multi node bus is required, EL602x should be selected; If the site is an RS232 device, select EL600x. EL6021-0021 is designed specifically for multi EL602x parallel scenarios, and its higher bias resistance can avoid bus level abnormalities caused by parallel bias resistance.

Precautions for Mechanical Installation and E-Bus Power Supply

The EL600x/EL602x adopts a standard 12mm or 26mm (dual channel) width housing and is installed on a 35mm DIN rail (compliant with EN60715). Attention should be paid during installation:

No communication module limitation: In the same I/O station, it is not allowed to install more than two "no communication modules" that do not participate in E-Bus data transmission in parallel, otherwise it will affect the reliability of data transmission.

E-Bus current consumption: EL6001 typical 120mA, EL6021 typical 170mA, EL6002 typical 170mA, EL6022 typical 250mA. It is necessary to ensure that the bus coupler (maximum 2A) or E-Bus power module (such as EL9410) can provide sufficient current. TwinCAT System Manager will automatically calculate and prompt for insufficient power supply (display exclamation mark).

Grounding and shielding: The terminal module provides shielding connection points (FE) for eliminating EMC interference. It is strictly prohibited to use functional grounding for releasing residual current or potential difference - the shielding layer is only used for releasing high-frequency interference and cannot replace protective grounding.

Wiring points: RS422/RS485 terminal and bias resistor

The physical layer wiring of RS422/RS485 is the most error prone link in on-site debugging, and its core lies in the reasonable configuration of terminal resistors and bias resistors.

3.1 Terminal Resistance

RS422 (full duplex, point-to-point or multi-point reception): A 120 Ω terminal resistor must be connected across the receiving end (RxD+/RxD -). It is recommended to use a clear linear topology with as short branches as possible.

RS485 (half duplex, multi station bus): The terminal resistor is only placed at the devices at both ends of the bus, and the intermediate node is not connected to the terminal. Each terminal resistance is 120 Ω.

3.2 Bias resistor (unique to EL602x)

When the bus is idle, the differential lines (A/B or T+/T -) need to maintain a certain level to prevent false triggering. EL602x has an integrated bias resistor (pull up to power, pull down to ground). But if multiple EL602x are connected in parallel in the bus, the bias resistance of the parallel connection will be too small, which will increase the bus load and may cause abnormal voltage levels. At this point, EL6021-0021 (with increased bias resistance) should be placed in the middle of the bus as a "relay" node to reduce the overall bias current.

3.3 Definition of Wiring Pins (Single Channel EL6021)

Terminal 1: TxD+(sending positive)

Terminal 5: TxD - (Send Negative)

Terminal 2: RxD+(receive positive)

Terminal 6: RxD - (receive negative)

Terminal 3/7: GND (internal short circuit)

Terminal 4/8: Shielding (internal short circuit)

The dual channel EL6022 uses a DE9 female header, and the pin allocation is detailed in the document (channel 1: Pin2 Tx+, Pin3 Rx+, Pin7 Tx -, Pin8 Rx -); Channel 2 is similar).

3.4 Half Duplex/Full Duplex Mode Settings

EL602x supports configuration through the combination of CoE objects x800:06 (Enable half duplex) and x800:07 (Enable point to point connection):

00: RS485 half duplex, the terminal module will receive the data it sends (requiring software filtering).

01: RS422 full duplex, point-to-point (default).

10: RS485 half duplex, the terminal module only receives data from other devices (not its own data).

11: RS422 full duplex, but only enables reception after transmission is complete (to avoid echo).

In practical applications, if RS485 multi station is used, mode 10 is usually selected.

TwinCAT debugging process (from scanning to parameterization)

4.1 ESI Device Description File Update

Firstly, ensure that the ESI directory of TwinCAT contains the latest XML description files for EL600x/EL602x. You can download it online through TwinCAT's "Update Device Description File (via ETG website)" function, or download it from Beckhoff's official website and put it in C: TwinCAT 3.1 Config Io EtherCAT. Attention: Different revision versions (such as -0016, -0019) may correspond to different hardware/firmware combinations and must be matched.

4.2 Online Scanning and Configuration

Switch TwinCAT to Config mode, right-click on "I/O Devices" → "Scan Devices", and select EtherCAT devices.

After scanning the terminal module, the system will automatically load the default process data (PDO). For EL6001/EL6021, the default PDO is 22 bytes of user data+1 byte of control/status (corresponding to RxPDO 0x1604 and TxPDO 0x1A04).

If you need a 16 bit process data interface (for 9-bit data or more efficient data transmission), you can select PDO 0x1605 (output extension) and 0x1A05 (input extension) in the "Process Data" tab. This requires firmware version support (EL6001 FW08 and above).

4.3 CoE parameter configuration (0x8000 object)

All communication parameters are concentrated in object 0x8000 (single channel) or 0x80n0 (dual channel, where n=0 is channel 1 and n=1 is channel 2). Key sub index:

0x8000:11 (baud rate): Supports 2400~115200, and can also input any integer value (1000~115200) directly through 0x8000:1B (Explicit baud). The firmware must be ≥ 11 (EL6001) or ≥ 09 (EL6021).

0x8000:15 (data frame): Optional formats include 7E1, 8N1, 8O2, etc., and special formats (such as 9N1) can also be selected through 0x8000:1C (Extended data frame).

0x8000:05 (transmission rate optimization): default enabled. When there are no new bytes within approximately 16 bits after receiving data, the buffer content is automatically packed into the process image to reduce the EtherCAT cycle burden. If the device sends continuously without any gaps, this function should be turned off.

0x8000:04 (Continuously Sending FIFO Data): When enabled, first fill the send buffer with up to 128 bytes, and then trigger continuous sending through the rising edge of the "Send continuous" bit of the control word until the buffer is empty.

0x8000:1A (Rx buffer full notification): Set the "Buffer full" status bit when the amount of data in the receive FIFO reaches 864 bytes by default.

Important: After modifying any of the above communication settings, reinitialization must be triggered through the control word (Init request), otherwise the changes will not take effect. Initialization process: Set Init request → Wait for Init accepted → Reset Init request.

Process data and control word analysis

5.1 Standard Process Image (22 Byte Mode)

Output (Controller → Terminal): Contains control words (low 8 bits or high 8 bits, depending on PDO selection) and up to 22 bytes of data (Data Out 0~21).

Input (Terminal → Controller): Contains a status word and up to 22 bytes of received data (Data In 0~21).

Control word key bits (taking single channel bitwise representation as an example):

Bit 0 (Transmit request): The controller is set to notify the terminal module that "Output length" bytes are waiting to be sent; The terminal module has received confirmation from the rear position 'Transmit accepted'.

Bit 1 (Receive accepted): Set the controller to confirm that the input data has been read; The terminal module can then send new data.

Bit 2 (Init request): Set to initiate initialization, enter ready after reset.

Bit 3 (Send continuous): When continuous transmission mode is enabled, the rising edge initiates FIFO transmission.

Status word key position:

Bit 0 (Transmit accepted): Terminal module confirms sending request.

Bit 1 (Receive request): The terminal module is set to indicate the presence of new received data (length indicated by "Input length").

Bit 2 (Initialize accepted): Initialization completed.

Bit 3 (Buffer full): Receive FIFO full, subsequent data loss.

Bit 4~6: Parity check error, frame error, over limit error.

Bit 8~15: Input length (actual number of received bytes).

5.2 Data Transmission Handshake Process

Send (controller → terminal):

Set the 'Output length' to the number of bytes to be sent (n).

Fill in Data Out 0~n-1.

Set 'Send request'.

Wait for the terminal module to be set to 'Transmit accepted'.

Reset 'Send request' (can be reset immediately, terminal module has locked data).

Reception (terminal → controller):

Waiting for 'Receive request' to be set.

Read the 'Input length' and data area.

Set 'Receive accepted' to confirm.

Reset the terminal module to 'Receive request' (prepare for the next frame).

Common Troubleshooting Ladder Table

Possible causes of fault phenomena, priority troubleshooting steps, advanced measures

The terminal module cannot enter the OP state due to ESI version mismatch or PDO configuration error. Check the EtherCAT state machine and check the AL status code; Rescan and verify the revised version to check if the CoE in the Startup List is written correctly; Restore factory default (0x1011:01 Write 0x64616F6C)

Serial port has no data receiving baud rate/data frame mismatch; Wiring error (RS485 polarity reversed) Use an oscilloscope to measure Tx/Rx levels; Confirm that the setting of CoE 0x8000:11/15 is consistent with the device and check if the terminal resistance is missing (RS422 remote requires 120 Ω); Check the 'Enable half duplex' mode

Data reception garbled or byte loss transmission rate optimization turned off, resulting in each byte being uploaded separately; EtherCAT cycle too long to enable 0x8000:05; Shorten the cycle time or increase the receiving buffer threshold to check if the "Explicit Baudrate" frequency error is less than 0.6% (using integer baud rate)

RS485 bus communication conflict: Improper half duplex mode setting. The terminal module receives data sent by itself and sets x800:06=1 (half duplex) and x800:07=0, and sets mode 10 to check the bus terminal resistance position; Confirm that only two end devices are connected to the terminal

Failed to send data. Send buffer full (128 bytes). Check if "Send continuous" is enabled; Confirm the completion of the 'Send accepted' handshake to increase the EtherCAT cycle time and give the terminal more processing time

TwinCAT scans for unknown devices with missing or outdated ESI files. Use 'Update Device Descriptions' to obtain the latest ESI. Check' Show Hidden Devices' and select compatible revision versions

After firmware update, the module does not respond. Download incompatible firmware or interrupt to try to re-enter BOOTSTRAP mode (see below). If there is no response, return to the factory for repair

Firmware updates and version compatibility

The firmware and hardware versions of EL600x/EL602x must match. The document lists a detailed compatibility table (EL6001 HW03-17 can run FW05~16). Important rule: High version firmware is usually backward compatible with lower version hardware, but the opposite is not necessarily true. Before updating, it is necessary to confirm the hardware version (see shell serial number or CoE 0x1009).

Firmware update steps (TwinCAT):

Set TwinCAT to Config/FreeRun mode.

Switch from the station to BOOTSTRAP mode (via the "Bootstrap" button on the Online tab).

In "EtherCAT" → "Advanced Settings" → "ESC Access" → "Firmware Update", select the. efw file (if it is bundled firmware, password=1 can update ESI at the same time).

Wait for the progress to be completed, do not turn off the power or network.

Switch back to Initiat → PREOP, power off and restart the module, check CoE 0x100A to confirm the new firmware version.

FPGA firmware update (*. rbf) is applicable to terminal modules with FPGA (such as early EL6001). The operation path is similar, but it is necessary to confirm that the FPGA version is ≥ 10 (E-Bus terminal) before updating online, otherwise it needs to be returned to the factory.

Factory reset: Double click 0x1011:01 in CoE Online, write the hexadecimal value 0x64616F6C (ASCII "load"), and restore all backup objects to their default settings. If the terminal module is older (before 2007), you can try 0x6C6F6164.

Advanced features: LIN master station support and command mode

8.1 LIN master station auxiliary function of EL6001 (FW10 and above)

EL6001 can simulate LIN bus master station frame transmission at RS232 level. Enabling method: Write 0x3000 in CoE 0x8000:01 (command object), and then the terminal module will automatically insert a 13 bit synchronization interrupt and synchronization byte 0x55 before sending data. Automatically remove these fields upon receipt. This feature does not include a complete LIN protocol stack and only provides physical layer assistance. It requires the PLC to implement PID and checksum calculations. An additional RS232-LIN level converter is required for use.

8.2 Command Mode (MultiDataFrame)

EL6021 FW06 and above support switching encoding modes during the transmission process. For example, the first n bytes use Mark Parity, and subsequent bytes use Space Parity. Write specific values through command object 0xB000 (0x2001 enables multi frame, 0x2100+encoding A, 0x2200+n, 0x2300+encoding B), and then trigger Send continuous sending.

Notes on TwinCAT Virtual Serial COM Driver

If using EL60xx as a standard COM port for Windows (via TcVirtualComDriver), please note:

The upper level application (such as serial debugging assistant) will set the baud rate/data frame by itself, which will override the parameters in the CoE. Therefore, ensure that the driver version supports the required baud rate (1.18 and above support Explicit baud).

If opening the COM port fails, check the CoE error message in the ADS recorder, which may be an unsupported baud rate combination.

Maintenance and environmental disposal

Cleaning: Use only a soft cloth dipped in glass cleaner or alcohol to wipe the front panel, and do not use compressed air, steam, or abrasives.

Scrap: Dispose of according to electronic waste regulations, recycle circuit boards and electronic components separately, and send plastic parts for plastic recycling.