RS485 Modbus Relay PRO

RS485 Modbus Relay PRO RS485 Modbus Relay PRO(1, CB, Opto) RS485 Modbus Relay PRO(2, CB, Opto) RS485 Modbus Relay PRO(3, CB, Opto) RS485 Modbus Relay PRO(4, CB, Opto) RS485 Modbus Relay PRO(8, CB, Opto)

Information Categories: Relay Brand: Diustou

Description Features RS485 Modbus Relay Interfaces RS485

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Product Overview

• A relay is an electrical control device that causes a controlled quantity within an electrical output circuit to undergo a predetermined step change when the variation of the input quantity (excitation quantity) meets specified requirements. It establishes an interactive relationship between the control system (also known as the input circuit) and the controlled system (also known as the output circuit). Typically used in automated control circuits, it essentially functions as an "automatic switch" where a small current controls the operation of a larger current. Therefore, in circuits, it plays roles such as automatic regulation, safety protection, and circuit conversion.

Product Features

• 

User Instructions

• If the relay cannot be controlled by sending commands, try the following steps
  • Insert a clear command: 0d 0a 0d 0a 0d 0a 0d 0a between control commands
  • The delay between commands should be greater than 20ms
• The output terminal of the relay is equivalent to an electronic switch and does not output current or voltage itself.
• When the load connected to the relay output terminal has a high power or is an inductive load, it is recommended to add an RC snubber circuit at the load end to reduce the interference on the relay contacts during the switching process.

Host Computer Testing

• Connecting the Serial Port
  • Connect the relay module to the USB-to-485 module with the connection: A - A, B - B. GND can be left unconnected.
  • Open the Host Computer.
    • 
    • Refresh the serial port.
    • Select the corresponding serial port.
    • Select baud rate 9600.
    • Open the serial port.

• Setting the Communication ID
  • If there is only one module on the 485 bus, you can click the "Read ID" button to automatically read the module's ID and display it in the ID text box (in hexadecimal format). You can also set the module's ID to the value in the ID text box (in hexadecimal format) by clicking the "Set ID" button. The set module ID will be saved in the module and retained even after power-off.
    • 
  • If there is more than one module on the 485 bus, you cannot use the above method to read or set the ID. You must manually enter the ID of the module you wish to communicate with into the ID text box (in hexadecimal format) to operate the corresponding module. If the ID is set to 0, it is in broadcast mode, and all modules on the bus will receive the same command and perform the same action, but there may be conflicts in the response commands, leading to unexpected results.
    • 

• Operating the Relay
  • You can operate the relay on the corresponding channel or turn all relays on/off simultaneously using the relay control buttons. The output status indicator for the corresponding channel will update accordingly upon receiving a response from the module.
    • 

• Debugging Function
  • The debugging area displays the command data (in hexadecimal format) currently being sent and received by the serial port. Click the "Send Directly" button to send the data in the "Send Data" text box via the serial port. Click the "Calculate CRC" button to automatically calculate the CRC for all data in the "Send Data" text box and append the result to the end, facilitating Modbus command debugging. Note: Since the sent command already includes the CRC, if you manually modify the command to be sent, you need to delete the last two bytes before clicking the "Calculate CRC" button.
    • 

Introduction to Modbus RTU Commands

• Modbus devices execute relevant operations by receiving Modbus RTU commands from external control terminals (such as host computers/MCUs). A frame of commands generally consists of the device address, function code, register address, register data, and checksum. The frame length is related to the function code. Typically, the first byte of each frame of data is the device address, with a settable range of 1-255 and a default of 255 (i.e., 0xFF). The last two bytes are the CRC checksum.
• Assuming the device address is 255, the commonly used Modbus RTU commands are as follows. For details, please refer to Module User Manual.

• Turn On Relay 1

Send: 	FF 05 00 00 FF 00 99 E4 
Return: FF 05 00 00 FF 00 99 E4 

Note 1: The 3rd and 4th bytes of the sent frame represent the relay address. The addresses for relays 1 to 8 are 0x0000, 0x0001, 0x0002, 0x0003, 0x0004, 0x0005, 0x0006, and 0x0007, respectively.

Note 2: The 5th and 6th bytes of the sent frame represent the data. 0xFF00 represents turning on the relay, and 0x0000 represents turning off the relay.

• Turn Off Relay 1

 
Send: 	FF 05 00 00 00 00 D8 14
Return: FF 05 00 00 00 00 D8 14 

• Turn On All Relays

 
Send: 	FF 0F 00 00 00 08 01 FF 30 1D 
Return: FF 0F 00 00 00 08 41 D3 

• Turn Off All Relays

Send:	 FF 0F 00 00 00 08 01 00 70 5D 
Return:	 FF 0F 00 00 00 08 41 D3 

• Set Device Address to 255

Send: 	00 10 00 00 00 01 02 00 FF EB 80 
Return:	00 10 00 00 00 01 02 00 FF EB 80 

Note: The 8th and 9th bytes of the sent frame, 0x00FF, represent the device address to be written.

• Read Device Address 255

 
Send: 	00 03 00 00 00 01 85 DB 
Return: 00 03 02 00 FF C5 C4
 

Note: The 4th and 5th bytes of the response frame, 0x00FF, represent the read device address.

• Set Baud Rate to 9600

 
Send:	FF 10 03 E9 00 01 02 00 03 8B CC 
Return: FF 10 03 E9 00 01 C5 A7
 

• Read Relay Status

 
Send: 	FF 01 00 00 00 08 28 12
Return: FF 01 01 01 A1 A0 

Generating Checksum

When sending module commands through ready-made host software, the CRC checksum is automatically generated. If you want to test the Modbus relay module using a serial port debugging software (such as SSCOM), you need to manually generate the CRC checksum and append it to the end of the transmission frame. For example, to open the first relay (manual mode):

• The transmission frame for opening/closing the relay (manual mode) consists of: Device address (1Byte) + Function code (1Byte) + Register address (2Byte) + Register data (2Byte) + CRC checksum (2Byte)
• Assuming the device address is 0xFF, the first 6 bytes of the transmission frame would be: FF 05 00 00 FF 00
• Use a CRC checksum tool to calculate the checksum for these 6 bytes: http://www.ip33.com/crc.html

• Swap the high and low bytes of the calculated checksum result E499 to obtain the CRC checksum 99E4, and the complete transmission frame: FF 05 00 00 FF 00 99 E4
• Send this transmission frame to the Modbus relay module through the serial port debugging software SSCOM V5.13.1 to open the first relay (manual mode), as shown below:

References

• Host Computer
• Module User Manual

Precautions

• Please use the power supply and load within the specified parameters and avoid exceeding them.
• The rated load and lifespan are reference values and may vary significantly depending on different environmental factors, load properties, and types. Therefore, it is best to confirm them in actual or simulated actual use.
• The module's load capacity is significantly affected by ambient temperature and its own temperature rise. It needs to be installed in an environment with good air convection for heat dissipation.
• Electrical endurance at high temperatures: When the module is used at high temperatures, its electrical endurance will be lower than at normal temperatures. Therefore, please confirm this in actual use.