VB中modbus tcp 示例

在VB中使用Modbus TCP进行通信的示例代码如下：

Imports System.Net.Sockets

Public Class Form1
    Dim client As TcpClient
    Dim stream As NetworkStream

    Private Sub btnConnect_Click(sender As Object, e As EventArgs) Handles btnConnect.Click
        Try
            client = New TcpClient(txtIPAddress.Text, Integer.Parse(txtPort.Text))
            stream = client.GetStream()
            MessageBox.Show("Connected to Modbus TCP device.")
        Catch ex As Exception
            MessageBox.Show("Connection failed: " & ex.Message)
        End Try
    End Sub

    Private Sub btnRead_Click(sender As Object, e As EventArgs) Handles btnRead.Click
        If client IsNot Nothing AndAlso client.Connected Then
            Try
                Dim request As Byte() = {0, 3, 0, 0, 0, 2, 197, 209} ' Modbus TCP Read Holding Register command
                stream.Write(request, 0, request.Length)

                Dim response(8) As Byte
                stream.Read(response, 0, response.Length)

                ' Process the response data
                Dim value As Integer = response(3) * 256 + response(4)
                MessageBox.Show("Read value: " & value.ToString())
            Catch ex As Exception
                MessageBox.Show("Read failed: " & ex.Message)
            End Try
        Else
            MessageBox.Show("Not connected to Modbus TCP device.")
        End If
    End Sub

    Private Sub btnDisconnect_Click(sender As Object, e As EventArgs) Handles btnDisconnect.Click
        If client IsNot Nothing AndAlso client.Connected Then
            stream.Close()
            client.Close()
            MessageBox.Show("Disconnected from Modbus TCP device.")
        End If
    End Sub
End Class

这个示例代码演示了通过VB中的TCPClient类实现与Modbus TCP设备的通信。在点击"Connect"按钮后，会尝试连接到指定的Modbus TCP设备。在点击"Read"按钮后，会发送Modbus TCP的读保持寄存器命令，并接收并处理设备返回的数据。在点击"Disconnect"按钮后，会断开与Modbus TCP设备的连接。

请注意，此示例仅演示了基本的连接、读取和断开连接操作，实际使用中可能需要根据具体的Modbus设备和数据进行相应的命令编码和数据解析。