Modbus RTU Relay 4CH

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Overview

Modbus RTU Relay 4CH
Modbus RTU Relay 4CH

RS485 relay module
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Electrical Safety Precautions

  • This product should be operated and used by professional electricians or technical personnel. During use, please ensure electrical safety and take protective measures such as anti-leakage and insulation.
  • Before installing, maintaining, or replacing relay equipment, make sure to turn off the power and unplug the device.
  • Do not attempt to dismantle relay equipment to avoid damaging the device or risking electric shock.
  • Please properly install and place the relay equipment. Avoid using it in damp, overly hot, or flammable environments to prevent safety accidents due to improper installation or use.

Specifications

Power Supply DC 7~36V
Communication Interface RS485
Communication Baudrate 4800，9600，19200，38400，57600，115200，128000，256000
Default Communication Format 9600, N, 8, 1
Relay Channels 4 Channels
Relay Type High-power relay
Contact Form 1NO 1NC
Contact Load ≤30A 250V AC 或 ≤30A 28V DC
Modbus Protocol Standard Modbus RTU protocol
RS485 Address Setting 1~255
Indicator STA: MCU indicator, keep flashing when MCU normally working
TXD: Transmit Data indicator, lights up when sending data
RRXD: Receive Data indicator, lights up when receiving data

Hardware Connection

  • Connect the USB TO 485 to the target boards via cables, A-A and B-B connected as shown below:

800px-Modbus-RTU-Relay-4CH-details-11.jpg

Example Demonstration

The demo shows how the following two software operate.
SSCOM serial port debugging assistant is more convenient to operate, free of installation, and more convenient for complete display and analysis of instructions, but the disadvantage is that the data is not intuitive.
Modbus Poll software is directly operated on the register, and the data display is more convenient to observe, but the disadvantage is that the instruction is not displayed completely, so you need to be familiar with the Modbus register operation.
You can test using any method. It is recommended to use the SSCOM serial port debugging assistant software for the first test.

SSCOM Serial Port Debugging Assistant

  • Download SSCOM Serial port debugging assistant and open it on the computer, open the corresponding port number, and set the baud rate as 9600. Click Multi-Char to open the Send Multi-Char window, and click the function to send the corresponding command.

Modbus-RTU-Relay-2.png

  • If you need to send other commands, choose SendHEX. For checksum validation, select ModbusCRC16. After entering the first six bytes of the command, clicking SEND will automatically add the CRC check code.

Modbus-RTU-Relay-3.png

  • For detailed control commands, please see the development protocol.

Modbus Poll Software

  • The serial port software is not convenient to observe the data, you can choose Modbus Poll software to read the data. Download and install the Modbus Poll software.
  • Open the software, select Setup->Read/Write Definition, select the actual device address for Slave ID, select 01 Read Coils function code for Function, and change Quantity to 4 channels. Click OK to confirm.

600px-Modbus-RTU-Relay-4CH-1.jpg

  • Select Connection->Connect..., choose the corresponding serial port, set the baud rate to 9600, and select 8 Data bits and None Parity. Click OK to connect.

Modbus-RTU-Analog-Input-3.png

  • After the connection is normal, you can check the current relay status. Select the corresponding channel, then double-click the status value to pop up the send page. Choose On or Off, then Click Send to control the relay opening and closing.

600px-Modbus-RTU-Relay-4CH-2.jpg

Development Protocol

Function Code Introduction

Function Code Description Note
01 Read coil status Read relay status
03 Read holding register Read the address and version
05 Write single coil Write single relay
06 Write single register Set the baud rate and address
0F Write multiple coils Write all relays

Register Address Introduction

Address (HEX) Address storage content Register value Permission Modbus Function Code
0x0000
……
0x0003		 Channel 1~4 relay address 0xFF00: relay on
0x0000: relay off
0x5500: relay toggle
 Read/Write 0x01, 0x05, 0x0F
0x00FF Control all relays 0xFF00: all relays on
0x0000: all relays off
0x5500: all relays toggle		 Write 0x05
0x0100
……
0x0103		 Channel 1~4 relay toggle 0xFF00: relay toggle
0x0000: relay unchanged
 Write 0x05, 0x0F
0x01FF All relays toggle 0xFF00: all relays toggle
0x0000: all relays unchanged
 Write 0x05
0x0200
……
0x0203		 Channel 1~4 relay flash on Interval time: data*100ms
Value: 0x0007, Interval time: 7*100MS = 700MS		 Write 0x05
0x0400
……
0x0403		 Channel 1~4 relay flash off Interval time: data*100ms
Value: 0x0007, Interval time: 7*100MS = 700MS		 Write 0x05
4x2000 UART Parameter The high eight bits indicate the parity mode: 0x00~0x02
The low eight bits indicate the baud rate mode: 0x00~0x07		 Read/Write 0x03, 0x06
4x4000 Device Address Directly store Modbus address
Device address: 0x0001-0x00FF		 Read/Write 0x03, 0x06
4x8000 Software Version Converting to decimal and then shifting the decimal point two places to the left will represent the software version
0x0064 = 100 = V1.00		 Read 0x03

Operation Command Introduction

Control Single Relay

Send code: 01 05 00 00 FF 00 8C 3A

Field Description Note
01 Device Address 0x00 indicates the broadcast address, 0x01-0xFF indicates the device address
05 05 Command Relay control
00 00 Address The register address of the relay to be controlled, 0x0000-0x0003
FF 00 Command 0xFF00: relay on;
0x0000: relay off;
0x5500: relay toggle
8C 3A CRC16 The CRC16 checksum of the first 6 bytes of data

Return code: 01 05 00 00 FF 00 8C 3A

Field Description Note
01 Device Address 0x00 indicates the broadcast address, 0x01-0xFF indicates the device address
05 05 Command Relay control
00 00 Address The register address of the relay to be controlled, 0x0000-0x0003
FF 00 Command 0xFF00: relay on;
0x0000: relay off;
0x5500: relay toggle
8C 3A CRC16 The CRC16 checksum of the first 6 bytes of data

For example: [Address 1 device]:

Relay 0 on: 01 05 00 00 FF 00 8C 3A
Relay 0 off: 01 05 00 00 00 00 CD CA
Relay 1 on: 01 05 00 01 FF 00 DD FA
Relay 1 off: 01 05 00 01 00 00 9C 0A
Relay 2 on: 01 05 00 02 FF 00 2D FA
Relay 2 off: 01 05 00 02 00 00 6C 0A
Relay 3 on: 01 05 00 03 FF 00 7C 3A
Relay 3 off: 01 05 00 03 00 00 3D CA
Relay 0 toggle: 01 05 00 00 55 00 F2 9A
Relay 1 toggle: 01 05 00 01 55 00 A3 5A
Relay 2 toggle: 01 05 00 02 55 00 53 5A
Relay 3 toggle: 01 05 00 03 55 00 02 9A

Control All Relays

Send code: 01 05 00 FF FF 00 BC 0A

Field Description Note
01 Device Address 0x00 indicates the broadcast address, 0x01-0xFF indicates the device address
05 05 Command Relay control
00 FF Address Fixed 0x00FF
FF 00 Command 0xFF00: relay on;
0x0000: relay off;
0x5500: relay toggle
BC 0A CRC16 The CRC16 checksum of the first 6 bytes of data

Return code: 01 05 00 FF FF 00 BC 0A

Field Description Note
01 Device Address 0x00 indicates the broadcast address, 0x01-0xFF indicates the device address
05 05 Command Relay control
00 FF Address Fixed 0x00FF
FF 00 Command 0xFF00: relay on;
0x0000: relay off;
0x5500: relay toggle
BC 0A CRC16 The CRC16 checksum of the first 6 bytes of data

For example: [Address 1 device]: 

All relays on: 01 05 00 FF FF 00 BC 0A
All relays off: 01 05 00 FF 00 00 FD FA
All relays toggle: 01 05 00 FF 55 00 C2 AA

Read Relay Status

Send code: 01 01 00 00 00 04 3D C9

Field Description Note
01 Device Address 0x00 indicates the broadcast address, 0x01-0xFF indicates the device address
01 01 Command Query relay status
00 00 Relay Start Address The register address of the relay, 0x0000 - 0x0003
00 04 Relay Number The number of relays to be read, which must not exceed the maximum number of relays
3D C9 CRC16 The CRC16 checksum of the first 6 bytes of data

Receive code: 01 01 01 00 51 88

Field Description Note
01 Device Address 0x00 indicates the broadcast address, 0x01-0xFF indicates the device address
01 01 Command Query relay status
01 Byte Number The number of all bytes of the returned status information
00 Query status Received relay status
Bit0: the first relay status;
Bit1: the second relay status;
And so on, with the idle high bit being zero
51 88 CRC16 The CRC16 checksum of the first 6 bytes of data

For example: [Address 1 device] 

Send: 01 01 00 00 00 08  3D CC
Receive: 01 01 01 00 51 88    //all relays off
Send: 01 01 00 00 00 08  3D CC
Receive: 01 01 01 01 90 48    //Relay 0 is on, others are off

Write Relay Status

Send code: 01 0F 00 00 00 04 01 0F 7E 92

Field Description Note
01 Device Address 0x00 indicates the broadcast address, 0x01-0xFF indicates the device address
0F 0F Command Write relay status
00 00 Relay Start Address The register address of the relay to be controlled, 0x0000 - 0x0003
00 04 Relay Number The number of relays to be operated, which must not exceed the maximum number of relays
01 Byte Number The byte number of the status
0F Relay Status Bit0: the first relay status;
Bit1: the second relay status;
And so on, with the idle high bit being zero
7E 92 CRC16 The CRC16 checksum of the first 6 bytes of data

Receive code: 01 0F 00 00 00 04 54 08

Field Description Note
01 Device Address 0x00 indicates the broadcast address, 0x01-0xFF indicates the device address
0F 0F Command Control all registers
00 00 Relay Start Address The register address of the relay to be controlled, 0x0000 - 0x0003
00 04 Relay Number The number of relays to be operated
54 08 CRC16 The CRC16 checksum of the first 6 bytes of data

For example: [Address 1 device] 

All relays on: 01 0F 00 00 00 04 01 0F 7E 92
All relays off: 01 0F 00 00 00 04 01 00 3E 96
0-1 on; 2-3 off: 01 0F 00 00 00 04 01 03 7E 97

Relay Flash ON/OFF Command

Send code: 01 05 02 00 00 07 8D B0

Field Description Note
01 Device Address 0x00 indicates the broadcast address, 0x01-0xFF indicates the device address
05 05 Command Single control command
02 Flash on flash off 02: flash on, 04: flash off
00 Relay Address The address of the relay to be controlled, 0x00~0x03
00 07 Interval Time The interval time: data*100ms
Value: 0x0007, Interval time: 7*100MS = 700MS
The maximum setting for the flash-on flash-off time is 0x7FFF
8D B0 CRC16 The CRC16 checksum of the first 6 bytes of data

Receive code: 01 05 02 00 00 07 8D B0

Field Description Note
01 Device Address 0x00 indicates the broadcast address, 0x01-0xFF indicates the device address
05 05 Command Single control command
02 Flash on flash off 02: flash on, 04: flash off
00 Relay Address The address of the relay to be controlled, 0x00~0x03
00 07 Interval Time The interval time: data*100ms
Value: 0x0007, Interval time: 7*100MS = 700MS
The maximum setting for the flash-on flash-off time is 0x7FFF
8D B0 CRC16 The CRC16 checksum of the first 6 bytes of data

For example: [Address 1 device] 

Relay 0 flash on: 01 05 02 00 00 07 8D B0  //700MS = 7*100MS = 700MS
Relay 1 flash on: 01 05 02 01 00 08 9C 74  //800MS
Relay 0 flash off: 01 05 04 00 00 05 0C F9  //500MS
Relay 1 flash off: 01 05 04 01 00 06 1D 38  //600MS

Set Baudrate Command

Send code: 01 06 20 00 00 05 42 09

Field Description Note
01 Device Address 0x00 indicates the broadcast address, 0x01-0xFF indicates the device address
06 06 command Set the baud rate and device address
20 00 Baud rate register 0x2000: set the baud rate
00 Parity Method x00: no parity, 0x01: even parity; 0x02: odd parity
05 Baud Rate Value Corresponding baud rate
0x00: 4800
0x01: 9600
0x02: 19200
0x03: 38400
0x04: 57600
0x05: 115200
0x06: 128000
0x07: 256000
42 09 CRC16 The CRC16 checksum of the first 6 bytes of data

Receive code: 01 06 20 00 00 05 43 D8

Field Description Note
01 Device Address 0x00 indicates the broadcast address, 0x01-0xFF indicates the device address
06 06 command Set the baud rate and device address
20 00 Baud rate register 0x2000: set the baud rate
00 Parity Method x00: no parity, 0x01: odd parity; 0x02: even parity
05 Baud Rate Corresponding baud rate
0x00: 4800
0x01: 9600
0x02: 19200
0x03: 38400
0x04: 57600
0x05: 115200
0x06: 128000
0x07: 256000
42 09 CRC16 The CRC16 checksum of the first 6 bytes of data

For example: [Address 1 device] 

Set the baud rate as 4800: 01 06 20 00 00 00 82 0A
Set the baud rate as 9600: 01 06 20 00 00 01 43 CA
Set the baud rate as 115200: 01 06 20 00 00 05 42 09

Set Device Address Command

Send code: 01 06 40 00 00 01 5D CA

Field Description Note
01 Device Address 0x00 indicates the broadcast address, 0x01-0xFF indicates the device address
06 06 command Set the baud rate and device address
40 00 Device address register 0x4000: set the device address
00 01 Device Address Set the device address, 0x0001-0x00FF
5D CA CRC16 The CRC16 checksum of the first 6 bytes of data

Receive code: 01 06 40 00 00 01 5D CA

Field Description Note
01 Device Address 0x00 indicates the broadcast address, 0x01-0xFF indicates the device address
06 06 command Set the baud rate and device address
40 00 Device address register 0x4000: set the device address
00 01 Device Address Set the device address, 0x0001-0x00FF
5D CA CRC16 The CRC16 checksum of the first 6 bytes of data

For example: [Address 1 device] 

Set the device address as 0x01: 00 06 40 00 00 01 5C 1b
Set the device address as 0x02: 00 06 40 00 00 02 1C 1A
Set the device address as 0x03: 00 06 40 00 00 03 DD DA

Read Device Address Command

Send code: 00 03 40 00 00 01 90 1B

Field Description Note
00 Device Address 0x00 indicates the broadcast address, 0x01-0xFF indicates the device address
03 03 Command Read the device address
40 00 Device address register 0x4000: read the device address
00 01 Byte Number Fixed 0x0001
90 1B CRC16 The CRC16 checksum of the first 6 bytes of data

Receive code: 00 03 02 00 01 44 44

Field Description Note
00 Device Address 0x00 indicates the broadcast address, 0x01-0xFF indicates the device address
03 03 Command Read the software version and device address
02 Byte Number The number of bytes returned
00 01 Device Address Set the device address, 0x0001-0x00FF
44 44 CRC16 The CRC16 checksum of the first 6 bytes of data

For example: [Address 2 device] 

Send: 00 03 40 00 00 01 90 1B
Receive: 00 03 02 00 02 04 45     //Address: 0x02

Read Software Version Command

Send code: 01 03 80 00 00 01 AD CA

Field Description Note
01 Device Address 0x00 indicates the broadcast address, 0x01-0xFF indicates the device address
03 03 Command Read the software version and device address
80 00 Software version register 0x4000: read the device address, 0x8000: read software version
00 01 Byte Number Fixed 0x0001
AD CA CRC16 The CRC16 checksum of the first 6 bytes of data

Receive code: 01 03 02 01 2C B8 09

Field Description Note
01 Device Address 0x00 indicates the broadcast address, 0x01-0xFF indicates the device address
03 03 Command Read the software version and device address
02 Byte Number The number of bytes returned
01 2C Software Version Converting to decimal and then shifting the decimal point two places to the left will represent the software version


0x012C = 300 = V3.00

B8 09 CRC16 The CRC16 checksum of the first 6 bytes of data

For example: 

Send: 01 03 80 00 00 01 AD CA
Receive: 01 03 02 01 2C B8 09       //0x012C = 300 =V3.00

Exception Function Code

When the received command is incorrect or the device is abnormal, an exception response will be returned in the following format:

Receive: 01 85 03 02 91

Field Description Note
01 Device Address 0x00 indicates the broadcast address, 0x01-0xFF indicates the device address
85 Exception Function Code Exception function code = Request function code + 0x80
03 Byte Number Exception Code
02 91 CRC16 The CRC16 checksum of the first 6 bytes of data

An exception code is a single-byte value that indicates the type of error. Several commonly used exception codes defined by the Modbus protocol:

Exception Code Name Description
0x01 Illegal Function The requested function code is not supported
0x02 Illegal Data Address The requested data address is incorrect
0x03 Illegal Data Value The requested data value or operation cannot be executed
0x04 Server Failure Server equipment failure
0x05 Response The request has been received and is being processed
0x06 Device Busy The device is currently busy and cannot perform the requested operation


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