Troubleshooting Guide: Modbus 485 Communication Issues with Stepper/Brushless Motors

If you are trying to use the Modbus RTU protocol over RS-485 with RS-series stepper drivers or brushless motor drivers but encounter communication failures, follow these steps to diagnose and resolve the issue:

Check Hardware Connections

Example: CL57RS Stepper Driver

Ensure the RS-485 interface wiring is correct. Pay attention to the A (485+) and B (485-) lines and verify which wires they correspond to in the network cable (refer to the diagram below).
When using a network cable to connect to an RS485-USB converter, strictly follow the RS-series stepper driver manual for the correct pinout.

RS485 Communication Interface Pinout (CL57RS):

If using this [RS485-USB]() cable, connect:

Pin 1 → T/R+ (485+)

Pin 2 → T/R- (485-)

Pin 5 → GND



Example: BLD-510B Brushless Driver

RS485 Communication Interface Pinout (BLD-510B):





If using the same cable, follow the same wiring method.



Example: IDM-RS, ISV2, and ICL-RS Series

RS485 Communication Interface Pinout (IDM-RS/ISV2/ICL-RS):




If using the same cable, follow the same wiring method.



Verify Configuration Parameters

Ensure the baud rate, stop bits, parity, and data bits match the driver’s settings.

RS-Series Stepper Drivers

Confirm that the software’s baud rate matches the driver’s setting (refer to the diagram below).


Modbus address is set to 01 by default. If modified, ensure commands use the correct address.


Example: 01 06 62 00 00 41 56 42 (the first byte 01 is the Modbus address).

Use the provided RS232 debugging cable to verify the baud rate and address via software.


Brushless Drivers

All brushless drivers default to 9600 baud. Refer to the manual for details.


IDM-RS, ISV2, and ICL-RS Series

Similar to RS-series stepper drivers, settings can be adjusted via DIP switches (see the manual).

iDM-RS



ISV2



ICL-RS



Software Settings

Verify that the Modbus command format is correct, including:

Device address

Function code

Data field

CRC checksum

Test communication using example commands from the manual to rule out command errors.

Example Commands:

RS-Series Stepper Driver:

01 06 62 00 00 01 57 B2 → Sets PR0 mode to absolute positioning.

IDM-RS/ISV2/ICL-RS Series:

01 06 62 00 00 01 57 B2 → Sets PR0 mode to absolute positioning.

Brushless Driver:

01 06 80 00 09 02 27 9B → 2-pole pair startup.

Use Modbus Debugging Tools

Test communication using Modbus diagnostic tools (e.g., ModScan, Modbus Poll).

Manually send commands and check for responses to confirm successful communication.

Updated on: 28/03/2025