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docs: add project specs and documentation for Modbus relay control Initialize project documentation structure: - Add CLAUDE.md with development guidelines and architecture principles - Add project constitution (v1.1.0) with hexagonal architecture and SOLID principles - Add MCP server configuration for Context7 integration Feature specification (001-modbus-relay-control): - Complete feature spec for web-based Modbus relay control system - Implementation plan with TDD approach using SQLx for persistence - Type-driven development design for domain types - Technical decisions document (SQLx over rusqlite, SQLite persistence) - Detailed task breakdown (94 tasks across 8 phases) - Specification templates for future features Documentation: - Modbus POE ETH Relay hardware documentation - Modbus Application Protocol specification (PDF) Project uses SQLx for compile-time verified SQL queries, aligned with type-driven development principles.
2025-12-21 18:19:21 +01:00
# Modbus POE ETH Relay
Parsed from https://www.waveshare.com/wiki/Modbus_POE_ETH_Relay
# Overview
## Hardware Description
### Hardware Connection
- Connect the Modbus POE ETH Relay to the LAN via a network cable, and supply power through the power port or the POE.
### Electrical and Relay Safety Instructions
- This product must be operated by professional electricians or qualified personnel. During use, ensure electrical safety, leakage protection, and proper insulation.
- Before installing, maintaining, or replacing the relay device, always turn off the power and unplug the device.
- Do not attempt to disassemble the relay device to avoid damage or the risk of electric shock.
- Properly install and place the relay device. Do not use it in humid, overheated, flammable, or explosive environments to prevent accidents caused by improper installation or use.
#### 1. Load Matching
- Ensure the relay's rated voltage and current match the load. Do not exceed the rated capacity.
- For inductive loads (motors, coils, lamps, etc.), the starting current may be much higher than the rated current. Choose a relay with sufficient current margin.
#### 2. Short Circuit and Overcurrent Protection
- Install a **fuse** or **circuit breaker** in the relay circuit to prevent damage due to short circuits or accidental overcurrent. - Ensure the load circuit has no short circuits during wiring, and select protection components with appropriate current ratings if necessary.
#### 3. Arc and Switching Protection
- Relay switching generates arcs, which can cause contact wear or welding.
- For inductive loads, it is recommended to use **RC snubber circuits** or **varistors** for arc suppression.
#### 4. Installation Environment
- Do not use the relay in humid, high-temperature, flammable, explosive, or dusty environments.
- Install the relay securely to avoid vibrations or shocks that may cause misoperation or damage.
#### 5. Power-Off Operation
- Always cut off power before maintenance, wiring, or replacing the relay to ensure personnel and device safety.
- Latching relays are only powered when changing state. Avoid strong vibrations or strong magnetic fields while the relay is unpowered.
#### 6. Status Confirmation
- After powering on, confirm or reset the relay status as needed to prevent abnormal operation caused by transportation, installation, or external disturbances.
- Avoid power interruption during relay operation to prevent uncertain status or contact damage.
#### 7. Regular Inspection
- Periodically inspect relay contacts, terminals, and insulation to ensure proper operation.
- If abnormal heating, odor, or burn marks are detected, immediately cut off power and replace the relay.
### Indicator Light Description
| Indicator | Status description |
| RUN indicator | Ethernet port running indicator, outputs a square wave with a period of 2 seconds when the Ethernet port working normally. |
| STA indicator | MCU indicator, blinking when the MCU working normally. |
| TXD indicator | Send indicator, lights up when sending data. |
| RXD indicator | Receive indicator, lights up when receiving data. |
| Green indicator on Ethernet port | The green indicator will be on when TCP connection is established, which can be used to determine whether the module has established a communication link with the host software. |
| Yellow indicator on Ethernet port | Data activity indicator, when data is transmitted through the Ethernet port, the yellow indicator changes its state, which can be used to determine if there is data transmission |
# Module Parameter Configuration
The module needs to set the module parameters before communication, such as IP address, serial port format, Modbus protocol, etc. There are two modes of setting parameters: Vircom software configuration and web configuration.
Vircom software configuration allows for setting more parameters, but requires software installation. Web configuration does not require installation, but you need to know the IP address first, and the configuration parameters are few. It is recommended to use Virom for configuration.
Note:
1. The configuration can be done in any way, and it is recommended to use Virom software for first test.
2. It is recommended to modify only the IP address for the first configuration, other parameters are not recommended to be modified. The serial port parameters must be the default parameters; modifying the serial port parameters will result in no communication.
3. The module supports both Modbus RTU and Modbus TCP protocols. In the Advanced Settings -> Transfer Protocol, you can choose "None", which means the Modbus RTU protocol. It is not recommended to modify during the first configuration.
4. The selected Modbus TCP protocol must be configured using the Virom software and set to a non-storage Modbus gateway, otherwise the communication will not be normal.
## Virom Software Mode Configuration
### General Settings
Connect the module to the hardware and connect it to the network. Run the VirCom software (the computer on which Vircom is installed must be on the same LAN as the module).
The operation is as follows:
- 1. Click `Device`
- 2. Click `Auto Search`
- 3. Software search recognizes the device connected to the LAN
- 4. Select the device, and then click `Edit Device` or double-click the searched device directly - 5. Set up the device parameters:
- Modify the "IP mode" to a static assigned address, set the IP address, note that the static IP address entered must not be used by other devices, and it needs to be on the same LAN as the computer.
- The working mode is TCP server. The serial port setting is 115200 by default and cannot be modified.
- The "Transfer Protocol" in "Advanced Settings" defaults to "None", which means using the Modbus RTU protocol; if you select "Modbus TCP protocol", then use the Modbus TCP communication protocol.
- Click on "More Advanced Settings..." and select the Modbus Gateway Type as a non-storage Modbus gateway.
- Modify the "IP mode" to a static assigned address, set the IP address, note that the static IP address entered must not be used by other devices, and it needs to be on the same LAN as the computer.
- 6. Once the settings are complete, click `Modify Setting`
- 7. Click `Restart Dev`, wait for the module to restart, and the new settings will take effect.
Note: It is recommended to modify only the IP address for the first configuration, and do not modify other parameters.
See the figure below for details:
Note: The default Modbus gateway type is storage type, which will automatically send query commands several times, which may cause the controller chip to fail to respond, resulting in no response to the query commands. Therefore, you need to set it as Multi-host non-storage type.
### Protocol Setting
Note: It is recommended to use the default Modbus RTU protocol for the first configuration and no modifications are needed.
Although the module transmits data through the network port, it supports two Modbus protocols: Modbus RTU and Modbus TCP. By default, data is transparently transmitted, i.e. using the Modbus RTU protocol.
#### Modbus TCP Protocol Settings
- The "Transfer Protocol" in the "Advanced Settings" can be set to "Modbus TCP protocol". In this case, the Modbus RTU protocol of the main controller will be converted to the Modbus TCP protocol and transmitted through the network port.
- In this case, the device port automatically changes to 502. Users can use the Modbus TCP tool to connect to the IP port 502 of the serial port server.
- Click on "More Advanced Settings..." and select the Modbus Gateway Type as a non-storage Modbus gateway.
#### Modbus RTU Protocol Settings
- Set "Transfer Protocol" in the "Advanced Settings" to "None", and change to use Modbus RTU protocol.
- Click on "More Advanced Settings..." and select the Modbus Gateway Type as a non-storage Modbus gateway.
Note: The default Modbus gateway type is storage type, which will automatically send query commands several times, which may cause the controller chip to fail to respond, resulting in no response to the query commands. Therefore, you need to set it as Multi-host non-storage type.
### Virtual Serial Port Setting
The module transmits data through a network port (TCP/UDP protocol). In order to enable users to use the PoE port communication even with developed serial port software, a virtual serial port needs to be added. If not needed, this part can be skipped.
- First, install the virtual serial driver Virtual serial port driver
- Run Vircom and the user program on the same computer.
- Vircom creates a virtual COM port and connects this COM port to the serial server. When the user program uses the COM communication, it can send data to the user's serial port device through the Vircom serial port server.
The following steps demonstrate this operation:
- Click on "Serial Port & Device Management" on the Vircom main interface, then click "Add" and select to add COM2 (Among them, COM2 is the newly emerging COM port on the computer).
- Then enter the device management and double-click the device that needs to be bound to COM2. As shown in the diagram, select COM2 from the Virtual Serial Port list in the top left corner. Then click on "Modify Setting" and then click on "Restart Device".
- Return to the main interface of Vircom. It can be seen that COM2 has been connected to the device whose IP is 192.168.1.200. In this case, the virtual serial port COM2 can be used instead of the network port for communication.
## WEB Configuration
Using Vircom, you can search for and configure device parameters in different network segments. For Web configuration, you must first ensure that the computer and the serial server are in the same IP segment, and you need to know the IP address of the serial server in advance.
But Web configuration can be done on any computer without Vircom. (Different products have different web interfaces, which can be switched between Chinese and English)
1. Enter the IP address of the serial server in the browser, such as http://192.168.1.200 to open the following web page
2. In the Password field, enter your password: The default login password is not set or is set to 123456. If no password is set, you can enter any password and click the Login button to log in. After setting the password to log in, the settings at "Modify Web Login Key" will take effect:
3. The serial server parameters can be modified on the web page that appears.
4. After modifying the parameters, click the "Submit" button.
Attention: The system has added webpage settings function by default when it leaves the factory. If the configuration interface page file is overwritten and the webpage cannot be opened, the webpage file needs to be downloaded again.
Please refer to RS485 TO ETH (B) Manual
# 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
Modbus RTU Command: The default configuration is the Modbus RTU command
- 1. Open the serial port debugging assistant window
- 2. Select TCPClient for port number
- 3. Modify the remote IP and port number according to the Vircom settings above
- 4. Click the "Connect" button to connect to the TCP server
- 5. The green light of the network port will light up when the connection is successful
- 6. Click Multi-Char to open the Send Multi-Char window, the default display is the Modbus RTU command, click the corresponding function to send the corresponding command.
- 7. If you use the custom input box below to send the command, you need to set Verify as ModbusCRC16
Configure Modbus TCP Directives: If you want to set it as a Modbus TCP Directive, you need to change the commands
- 1. Click on the Import ini button in the Send Multi-Char column
- 2. Select the modbus tcp.ini file to import the Modbus TCP command
Note: If a popup error message says "A component named HEX0 already exists", then you need to close and reopen the software, which will reload the files and refresh the buttons.
- 3. After successful import, the following is displayed, click on the function to send the corresponding command.
Note: Modbus tcp does not require CRC checksum, select None for Verify.
- For detailed Modubs commands, please see the development protocol.
### Modbus Poll Software
It is not convenient to use the SSCOM software for observing the data, you can select Modbus Poll software to read the data. Download and install the Modbus Poll software.
- 1. Open Modbus Poll software
- 2. 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 8 channels. Click OK to confirm.
- 3. If:
- you are using the Modbus RTU protocol, select Connection->Connect Setup, select Modbus RTU/ASCII Over TCP/IP for Connection, select RTU for Mode, and enter the correct IP address and port number. Click OK to connect.
- you are using the Modbus TCP protocol, select Connection->Connect Setup, select Modbus TCP/IP for Connection, and enter the correct IP address and port number. Click OK to connect.
4. 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.
# Demo
### Raspberry Pi
Connect the Raspberry Pi and the ModBus POE ETH Relay module to the same LAN.
Open the Raspberry Pi terminal and run the program by entering the following command:
```sh
sudo apt-get install unzip
wget https://files.waveshare.com/wiki/Modbus-POE-ETH-Relay/Modbus_POE_ETH_Relay_Code.zip
unzip Modbus_POE_ETH_Relay_Code.zip
cd Modbus_POE_ETH_Relay_Code
#modbus rtu protocol
vi modbus_rtu.py #Change the IP address and port number according to the actual situation
sudo python3 modbus_rtu.py
#modbus tcp protocol
vi modbus_tcp.py #Change the IP address and port number according to the actual situation
sudo python3 modbus_tcp.py
```
Note: To run this demo, you need to modify the demo file to change the IP address and port number to the actual IP address and port number of the ModBus POE ETH Relay.
# Modbus RTU Development Protocol V2
## 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 …… 0x0007 | Channel 1~8 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 …… 0x0107 | Channel 1~8 relay toggle address | 0xFF00: relay toggle / 0x0000: relay unchanged | Write | 0x05, 0x0F |
| 0x01FF | Control all relays toggle | 0xFF00: all relays toggle / 0x0000: all relays unchanged | Write | 0x05 |
| 0x0200 …… 0x0207 | Channel 1~8 relay flash on | Interval time: data×100ms / Value: 0x0007, Interval time: 7×100MS = 700MS | Write | 0x05 |
| 0x0400 …… 0x0407 | Channel 1~8 relay flash off | Interval time: data×100ms / Value: 0x0007, Interval time: 7×100MS = 700MS | Write | 0x05 |
| 4x4000 | Device Address | Directly store Modbus address / Device address: 0x0001 | Read | 0x03 |
| 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 | Fixed 0x01 |
| 05 | 05 Command | Relay control |
| 00 00 | Address | The register address of the relay to be controlled, 0x0000-0x0007 |
| 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 | Fixed 0x01 |
| 05 | 05 Command | Relay control |
| 00 00 | Address | The register address of the relay to be controlled, 0x0000-0x0007 |
| 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 | Fixed 0x01 |
| 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 | Fixed 0x01 |
| 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 08 3D CC
| Field | Description | Note |
|-------|---------------------|-------------------------------------------------------------------------------------|
| 01 | Device Address | Fixed 0x01 |
| 01 | 01 Command | Query relay status |
| 00 00 | Relay Start Address | The register address of the relay, 0x0000 - 0x0007 |
| 00 08 | Relay Number | The number of relays to be read, which must not exceed the maximum number of relays |
| 3D CC | 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 | Fixed 0x01 |
| 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 Send: 01 01 00 00 00 08 3D CC Receive: 01 01 01 41 91 B8 //Relay 0 and 6 are on, others are off
### Write Relay Status
Send code: 01 0F 00 00 00 08 01 FF BE D5
| Field | Description | Note |
|-------|---------------------|-----------------------------------------------------------------------------------------------------------|
| 01 | Device Address | Fixed 0x01 |
| 0F | 0F Command | Write relay status |
| 00 00 | Relay Start Address | The register address of the relay to be controlled, 0x0000 - 0x0007 |
| 00 08 | 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 |
| FF | Relay Status | Bit0: the first relay status; Bit1: the second relay status; And so on, with the idle high bit being zero |
| BE D5 | CRC16 | The CRC16 checksum of the first 6 bytes of data |
Receive code: 01 0F 00 00 00 08 54 0D
| Field | Description | Note |
|-------|---------------------|---------------------------------------------------------------------|
| 01 | Device Address | Fixed 0x01 |
| 0F | 0F Command | Control all registers |
| 00 00 | Relay Start Address | The register address of the relay to be controlled, 0x0000 - 0x0007 |
| 00 08 | Relay Number | The number of relays to be operated |
| 54 0D | CRC16 | The CRC16 checksum of the first 6 bytes of data |
For example: [Address 1 device]
All relays on: 01 0F 00 00 00 08 01 FF BE D5 All relays off: 01 0F 00 00 00 08 01 00 FE 95 0-1 on; 2-7 off: 01 0F 00 00 00 08 01 03 BE 94
### Relay Flash ON/OFF Command
Send code: 01 05 02 00 00 07 8D B0
| Field | Description | Note |
|-------|----------------|-------------------------------------------------------------------------------------------------------------------------------------------|
| 01 | Device Address | Fixed 0x01 |
| 05 | 05 Command | Single control command |
| 02 | Command | 02: flash on, 04: flash off |
| 00 | Relay Address | The address of the relay to be controlled, 0x00~0x07 |
| 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 | Fixed 0x01 |
| 05 | 05 Command | Single control command |
| 02 | Command | 02: flash on, 04: flash off |
| 00 | Relay Address | The address of the relay to be controlled, 0x00~0x07 |
| 00 07 | Interval Time | The interval time: data*100ms Value: 0x0007, Interval time: 7*100MS = 700MS |
| 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 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
### Read Software Version Command
Send code: 01 03 80 00 00 01 AD CA
| Field | Description | Note |
|-------|------------------|-------------------------------------------------|
| 01 | Device Address | Fixed 0x01 |
| 03 | 03 Command | Read Holding Register |
| 80 00 | Command register | 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 00 C8 B9 D2
| Field | Description | Note |
|-------|------------------|-------------------------------------------------------------------------------------------------------------------------------------------|
| 01 | Device Address | Fixed 0x01 |
| 03 | 03 Command | Read Holding Register |
| 02 | Byte Number | The number of bytes returned |
| 00 C8 | Software Version | Converting to decimal and then shifting the decimal point two places to the left will represent the software version 0x00C8 = 200 = V2.00 |
| B9 D2 | 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 00 C8 B9 D2 //0x00C8 = 200 =V2.00
### 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 |
## Modbus TCP Command Introduction
Here is a brief introduction to Modbus TCP and Modbus RTU protocol conversion using the above commands to open the first relay as an example.
- Modbus RTU command: 01 05 00 00 FF 00 8C 3A
| Field | Description | Note |
|-------|----------------|------------------------------------------------------------------------------------|
| 01 | Device Address | Fixed 0x01 |
| 05 | 05 Command | Relay control |
| 00 00 | Address | The register address of the relay to be controlled, 0x00, that is, the first relay |
| FF 00 | Command | 0xFF00: Relay on |
| 8C 3A | CRC16 | The CRC16 checksum of the first 6 bytes of data |
- Modbus TCP command: 00 00 00 00 00 06 01 05 00 00 FF 00
| Field | Description | Note |
|-------|----------------|------------------------------------------------------------------------------------|
| 00 00 | Message Label | Both be 0x00 |
| 00 00 | modbus Label | Must both be 0, which means this is Modbus communication |
| 00 06 | Byte Length | Indicates the number of all bytes that follow, followed by 6 bytes |
| 01 | Device Address | Fixed 0x01 |
| 05 | 05 Command | Relay control |
| 00 00 | Address | The register address of the relay to be controlled, 0x00, that is, the first relay |
| FF 00 | Command | 0xFF00: Relay on |
By comparing the commands above, we can observe that to convert a Modbus RTU command to Modbus TCP protocol, the CRC check is removed, and the command is prefixed with five 0x00 bytes followed by a byte representing the length.
## Advanced Applications
- Relay control through Alibaba Cloud MQTT
- Relay control through Waveshare Cloud
- Relay control through HTTP GET/POST
# Resources
### Software
- Vircom configuration software
- Virtual serial port driver
- Sscom software
- Modbus Poll software
- SecureCRT software
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