How to set Soft start RS485

- Jul 24, 2019-

RS485 Communication

Through the inbuilt RS485 standard interface, t比WSTR 3000 series soft starter can connect with PC and PLC and other hosts to conduct serial communication. The command of the host can control running or stop of the soft starter, monitor the running status of the soft starter and modify its functional data. Please refer to RS485 operation instructions for the detailed information of the communication. Remote operation, running command input, running status management, write-once of functional data of several soft starters can be conducted by means of the RS485 communication through computers to implement simplified operation during function codes input.

Major functions

1. Input of stop running command.

2. Monitoring of the running status

3. Real-time tracking (tabular display of the running infom诏tion)

4. Read-once, write-once and saving to files of function codes. Please consult our company separately for thecommunication software.

MODBUS communication protocol

1 Overview about Modbus RTU communication protocol

Modbus is a kind of serial asynchronous communication protocol with RS485 as the physical interface. Being designed for Modicon PLC, it has the structural features of PLC. In network control, it can read and write the PRS 3000 as if it were a PLC. It can project the start and stop control, status information (current, fault etc.) and function parameters to the holding register (4:XXX). Its read and write control shall be conducted through the PL master station.

1.1 Electrical interface

RS485 half duplex

Communication parameters: baud rate: 9600; 8 data bits; no check digit; I stop bit. 1.2 Format of the communication data:

Data format:


2 related settings of the soft starter

2.1 Address of the register


(1) Registers not listed above shall be illegal and shall not be written or read; otherwise the slave station will report an exception code to the controller.

(2) All data addresses are based on 40000, that is, the address of the coil relay is 0001 and address of 402567is 0 I OO(hexadecimal)

2.2 Supported codes

The soft starter supports the following codes only, and exception code 01 will be reported if other codes are used.


Code 03 shall be read through WORD only

2.3 Description of the register


For example, to start the soft starter form the slave station address 02, the controller will send 02 06 00 01 00 01, if the command is executed normally, code 02 06 00 01 00 01 will be returned. Whether the soft starter can start norn叫ly or not shall further be based on the status register. If there's any fault, send 02 06 00 01 00 04 to reset it.

Status register of register address 40002

The status register reflects the status of the soft starter; it is represented by one word.


E.g. Read the status register codes 02 03 00 02 00 01

If the starter is in the process of starting, codes 02 03 00 02 00 01 will be returned.

If any fault with the starter, codes 02 03 00 02 00 08 will be returned, and types of fault can be read according to 4. 4003 mean value of current (hexadecimal)

The value projects the three-phase actual mean value of current* 1 O(including a decimal number)

E.g. Read the current value

Send codes 02 03 00 02 00 0 I

If the current is 235 A, codes 02 03 02 09 2E will be returned (actual current value shall be the returned value/IO) 40004 fault codes (hexadecimal)

When the third number in status register is 1, it represents that the soft starter is in fault status. The fault codes shall be the same as those in 6. I

E.g.: send codes 02 03 00 04 00 01

If02 03 02 00 04 are returned, it indicates the current input phase loss (fault code 04)

Function parameters register 40XXX of the soft starter

40256-4027 4 are function registers, the corresponding address are OXO 100-0XO 112, the high byte address is O 1, the low byte address are OXOO-OX12, the corresponding function codes are FO-FL, consistent with the function code table 4.2. For example, address OX109 is corresponding to function code F9 (starting mode). These codes can be written and read. The usages are illustrated respectively:

Example 1 Read the value of function code F5 (current limiting value)

Send codes 02 03 01 05 00 01

The returned read value ofF5 function code 02 03 02 01 5 E indicates the current limiting value is 350% Example 2 Read function code FA (protection level)

Send codes 02 03 01 OA 00 01

The returned read value of FA function code 02 03 02 00 03 indicates the protection level is 3.

Example 3 Change the function code 05(starting current) of the soft starter to 250%

The host sends the codes 02 06 01 05 00 FA, the soft starter returns the codes 02 06 01 05 00 FA. If codes 02 86 03 are returned, it indicates that writing failure, maybe the starter is running.

3 Exception response


3.1 Illegal function code 01

Format of the master station inquiry message:


As O x 80 function code is not used in the protocol, so for the substation response:


3 .2 Illegal data address 02

Format of the master station inquiry message


As register address of the 04 function code is incorrect, so for the substation response:


3 .3 Illegal data value 03

Format of the master station inquiry message


Number of registers of function code 04 is incorrect, so for the substation response:


4 Notes for use

(1) The communication address, communication rate and verification mode must be the same as the communication settings of the controller.

(2) If no response data is received, please check the above parameter settings; check if the connection to 485 terminals is correct and if the CRC verification is correct.

(3) In the event of communication among several TGS5, 120 Q resistances should be connected at both AB ends of the last TGS5.

(4) When connected to other Modbus equipments, connection should be conducted as per the diagram below:


Special Tips:

All soft starting products are of device types in case of delivery. In order to make it convenient for installation and debugging of the set manufactures, the output protection of the device-type soft starter has been set as "standard" when delivery. In installation and debugging, the set manufacturer can directly use a small motor or use three lamps to form a star to work as the load, then starting, stop, control and other operations can be conducted. However, in practical application, please be sure to change the output protection to "advanced", and then the soft starter will possess the complete protection functions for phase loss, three-phase unbalance, over-current, overloading and so on. (Note: If the soft starter is reset to factory defaults, the output protection will be reset to "standard" again, so it will be necessary to set the protection level to "advanced" again). Please kindly note this.