Preface:

The E870-EG01 is an edge computing gateway independently developed by Chengdu Ebyte Electronic Technology Co., Ltd., featuring visual programming capabilities. In the previous article, we introduced two of its feature nodes: the Logic Conversion Node and the Cache Queue Node. This article continues with other feature nodes: the Modbus Request Node and Modbus Parsing Node. These two nodes are typically used together: the Request Node generates user-defined Modbus data, while the Parsing Node decodes response messages from Modbus devices, extracts data, and outputs results in the debugging window.

Introduction to Featured Nodes

1. Modbus Request Node

The function of this node is straightforward: configure the slave address, function code, register address, quantity, and type of an instruction within the node.

For example, to generate an instruction to read the 3rd coil of slave address 5, configure the node as follows:

  • Slave address: 5

  • Function code: 1 (Read Coils)

  • Register address: 2 (registers are 0-indexed)

  • Quantity: 1

  • Type: Bit

The node will then generate the instruction: 05 01 00 02 00 01 5D 8E (the checksum is automatically calculated by the node).

1.png

Once configured, the Serial Port Node can send the instruction output by this node to Modbus devices connected to the EG01, enabling remote control of Modbus devices. The node supports generating multiple commands by adding more register configurations. For instance, to read coils 2 and 3 simultaneously, add a new configuration with register address 3. The node will output two Modbus instructions in the order they were added.

2. Modbus Parsing Node

This node decodes response messages from Modbus devices and outputs data (e.g., coil statuses, register values) in the debugging window.

In practical applications, it is usually used with the Request Node to facilitate real-time reading of response messages. To ensure correct parsing, configure the node with the matching function code corresponding to the message type to be decoded.

2.pngExample: To read and parse 5 coils from slave address 5, you need to parse 5 response messages sequentially. This requires adding 5 Parsing Nodes with correct configurations (as shown in the diagram).

3.pngIf you do not use the Request Node and want to parse custom Modbus messages, simply input the response message into the Parsing Node and connect a Debug Node to output the decoded data.

Advanced Usage

Writing Parameters

The deployment method for reading parameters is similar across scenarios. Below is how to write parameters:

Writing a Single Coil

  1. Set the Modbus Request Node’s function code to 5 (Write Single Coil).

  2. Enter the target coil address.

  3. Use an Inject Node to input values (e.g., 0 or 1) into the Request Node.

  4. Since writing data does not require parsing responses, send the generated message directly to the Modbus device via the Serial Port Node.

4.png

Writing Multiple Coils

To write values to multiple coils simultaneously:

  1. Use an Inject Node with a payload formatted as text (e.g., 1 1 1 1 for 4 coils).

  2. Set the Request Node’s function code to 15 (Write Multiple Coils).

5.png

Register Writing

The process for writing to registers is similar to the above examples. For further clarification:

  • Click any node and check the Help Window on the right.

  • Click the "Details" link at the bottom of the help window to access detailed node documentation and numerous official examples, which can be imported directly for use.