Why Can't the Servo Motor Use Modbus 485 Communication?
If you are trying to communicate over RS-485 using the Modbus RTU protocol for your servo motor, but are having trouble, here are some steps to help you diagnose and resolve the problem:
Cause Analysis and Solutions
1.1. Check Hardware Connections:
Please ensure that the RS-485 interface cable is connected correctly, and pay attention to which wires A and B (or '485+' and '485-') correspond to the network cable, as shown in the figure.
When using a network cable to connect the RS485-USB cable, be sure to refer to the wire sequence of the 485 network port in the servo driver manual.
Taking the A6-RS series servo motor as an example, its RS485 communication interface line sequence is as follows:
If you use this RS485-USB cable RS485-1, please connect the blue wire to T/R+, the blue and green wires to T/R-, and the brown wire to GND.
Check Configuration Parameters
Make sure the Modbus address of the servo motor and controller is set correctly. If the addresses do not match, communication will not be established.
Verify whether the baud rate, stop bit, parity bit and data bit settings are consistent with the servo motor configuration.
Software Settings
Make sure that the serial port settings used by your software (such as Python scripts) match the settings of the servo motor.
Check whether the format of the Modbus command sent is correct, including device address, function code, data and CRC check.
4.Use of Modbus Tools
Use professional Modbus communication debugging tools, such as Modscan, Modbus Poll, etc. These tools can help you manually send and receive Modbus commands to verify whether the communication is normal.
Example Demonstration
In order to better help you solve the problem, we will explain in detail the RS485 communication settings of the A6-RS series and T6 series servo motors sold by STEPPERONLINE.
3.1. A6 Series Servo Motor
● First, prepare the network cable and RS485-USB cable for communication. Please connect according to the network port definition in the manual, as explained above. After that, plug one end of the network cable into the RS485 communication port of the drive, and the other end to the USB port on the PC.
● Check your PC serial port settings: right-click the start menu - find "Device Manager" - drop down "Port" - find "Serial Port" - right-click "Properties" - click "Port Settings". In this way, you can see what the baud rate/data bit value of your PC communication serial port is.
● Check the serial port settings of the A6 servo drive: check the default communication parameters (axis address/baud rate, etc.) in the manual.
After confirming the parameters in the manual, please verify the axis address, baud rate and other parameters through the A6 series software or the driver's panel buttons.
After confirmation, open your serial port software and set the serial port according to the serial port data value found above. After the serial port is successfully opened, you can send some sample codes for simple testing. If data is returned, the communication is successful. (See page P330 of the manual for sample code)
3.2. T6 Series Servo Motor
● First, prepare the network cable and RS485-USB cable for communication. Connect according to the network port definition in the manual. The communication port line sequence of T6 is as shown in the figure below.
Then, the green and white wires of the network cable are connected to T/R+, the green wire is connected to T/R-, and the brown wire is connected to GND. Then, plug one end of the network cable into the 485 communication port of the drive, and connect the other end to the USB port on the PC.
● Check your PC serial port settings: right-click the start menu - find "Device Manager" - drop down "Port" - find "Serial Port" - right-click "Properties" - click "Port Settings". In this way, you can see what the baud rate/data bit value of your PC communication serial port is.
● Check the serial port settings of the T6 servo drive: check the default communication parameters in the manual (the default values of PR5.29/PR5.30/PR5.31 are 5/2/1 respectively)
Then, open the parameter panel through the software connector driver of the T6 series servo motor, find "PR5 Special Settings", and check in turn whether the current values of PA5.29/PA5.30/PA5.31 are consistent with the default value 5/ in the manual. 2/1) consistent, if not, please modify it.
● After confirming that it is correct, open your serial port software and set the serial port according to the serial port data value found above. After the serial port is successfully opened, you can send some sample codes for simple testing. If data is returned, the communication is successful. (See page P132 of the manual for sample code)
Cause Analysis and Solutions
1.1. Check Hardware Connections:
Please ensure that the RS-485 interface cable is connected correctly, and pay attention to which wires A and B (or '485+' and '485-') correspond to the network cable, as shown in the figure.
When using a network cable to connect the RS485-USB cable, be sure to refer to the wire sequence of the 485 network port in the servo driver manual.
Taking the A6-RS series servo motor as an example, its RS485 communication interface line sequence is as follows:
If you use this RS485-USB cable RS485-1, please connect the blue wire to T/R+, the blue and green wires to T/R-, and the brown wire to GND.
Check Configuration Parameters
Make sure the Modbus address of the servo motor and controller is set correctly. If the addresses do not match, communication will not be established.
Verify whether the baud rate, stop bit, parity bit and data bit settings are consistent with the servo motor configuration.
Software Settings
Make sure that the serial port settings used by your software (such as Python scripts) match the settings of the servo motor.
Check whether the format of the Modbus command sent is correct, including device address, function code, data and CRC check.
4.Use of Modbus Tools
Use professional Modbus communication debugging tools, such as Modscan, Modbus Poll, etc. These tools can help you manually send and receive Modbus commands to verify whether the communication is normal.
Example Demonstration
In order to better help you solve the problem, we will explain in detail the RS485 communication settings of the A6-RS series and T6 series servo motors sold by STEPPERONLINE.
3.1. A6 Series Servo Motor
● First, prepare the network cable and RS485-USB cable for communication. Please connect according to the network port definition in the manual, as explained above. After that, plug one end of the network cable into the RS485 communication port of the drive, and the other end to the USB port on the PC.
● Check your PC serial port settings: right-click the start menu - find "Device Manager" - drop down "Port" - find "Serial Port" - right-click "Properties" - click "Port Settings". In this way, you can see what the baud rate/data bit value of your PC communication serial port is.
● Check the serial port settings of the A6 servo drive: check the default communication parameters (axis address/baud rate, etc.) in the manual.
After confirming the parameters in the manual, please verify the axis address, baud rate and other parameters through the A6 series software or the driver's panel buttons.
After confirmation, open your serial port software and set the serial port according to the serial port data value found above. After the serial port is successfully opened, you can send some sample codes for simple testing. If data is returned, the communication is successful. (See page P330 of the manual for sample code)
3.2. T6 Series Servo Motor
● First, prepare the network cable and RS485-USB cable for communication. Connect according to the network port definition in the manual. The communication port line sequence of T6 is as shown in the figure below.
Then, the green and white wires of the network cable are connected to T/R+, the green wire is connected to T/R-, and the brown wire is connected to GND. Then, plug one end of the network cable into the 485 communication port of the drive, and connect the other end to the USB port on the PC.
● Check your PC serial port settings: right-click the start menu - find "Device Manager" - drop down "Port" - find "Serial Port" - right-click "Properties" - click "Port Settings". In this way, you can see what the baud rate/data bit value of your PC communication serial port is.
● Check the serial port settings of the T6 servo drive: check the default communication parameters in the manual (the default values of PR5.29/PR5.30/PR5.31 are 5/2/1 respectively)
Then, open the parameter panel through the software connector driver of the T6 series servo motor, find "PR5 Special Settings", and check in turn whether the current values of PA5.29/PA5.30/PA5.31 are consistent with the default value 5/ in the manual. 2/1) consistent, if not, please modify it.
● After confirming that it is correct, open your serial port software and set the serial port according to the serial port data value found above. After the serial port is successfully opened, you can send some sample codes for simple testing. If data is returned, the communication is successful. (See page P132 of the manual for sample code)
Updated on: 31/10/2024
Thank you!