VB.NET使用S7.NET读写S7-1200变量报错求助

问题描述 #

在VB.NET中使用S7.NET库读取S7-1200的变量时持续报错，尝试了多种读取语法（代码中已注释的写法）均未解决。相关代码及PLC变量配置如下：

原代码 #

Option Strict Off
Option Explicit On
Imports S7.Net

Imports System.Data.SqlClient
Imports Microsoft.Reporting.WinForms
Imports System.Data
Imports VB = Microsoft.VisualBasic
Imports Microsoft.VisualBasic.PowerPacks
Imports System.Xml
Imports System.Text
Imports System.IO
Imports System.Security.Cryptography
Imports System.Threading
Module PLC_InOut
    Public Sub PLCInOuts()
        '  Dim Result As BitArray()

        ' Result = PLC.Read("DB8.DBW0")
        '\\\\\\\Inputs
        ' Result = PLC.Read(DataType.DataBlock, 8, 0, VarType.Bit, 0, 16)
        'Result = PLC.Read(DataType.DataBlock, 8, 0, VarType.Byte, 1, 0)
        ' Result = PLC.Read("DB7.DBX0.0")
        'Dim Value1 As Byte = PLC.Read("DB8.DBW0")
        Dim u1 As System.UInt16 = PLC.Read("DB8.DBW0")
        Dim b1() As Byte = BitConverter.GetBytes(u1)


        If test1_out Then

            '   PLC.Write(DataType.Output, 0, 0, VarType.Bit, True)
            'PLC.Write("O0.0", 1)
            'PLC.Write("%M47.6", True)
            '  PLC.Write("DB7.DBX0.0", True)
            'PLC.WriteBit(DataType.DataBlock, 7, 0, 0, True)
        End If
        ' ("db8.dbx0.0")
        '\\\\\\\outputs
        '   PLC.WriteBit(DataType.DataBlock, 7, 0, 0, test1_out)
    End Sub
End Module

PLC变量配置说明 #

PLC中DB8块包含字类型变量，DB7块包含位类型变量；需注意S7-1200默认开启优化的块访问，该模式会导致传统地址读取失败，需提前禁用。

解决方案 #

1. 初始化PLC连接对象 #

原代码缺失PLC实例的创建与连接步骤，这是核心问题之一。需先创建Plc对象并建立连接：

' 定义全局PLC实例
Private Shared PLC As Plc

' 初始化连接
Public Sub InitPlcConnection()
    ' S7-1200需指定S7ProtocolType.S1200
    PLC = New Plc(S7ProtocolType.S1200, "PLC实际IP地址", 0, 1)
    Try
        PLC.Open()
        If PLC.IsConnected Then
            Console.WriteLine("PLC连接成功")
        End If
    Catch ex As Exception
        Console.WriteLine("连接失败: " & ex.Message)
    End Try
End Sub

2. 正确的变量读取写法 #

根据S7.NET语法规范，结合S7-1200地址规则，提供两种可靠读取方式：

方式一：符号地址读取（需禁用优化块访问）

' 读取DB8.DBW0（字类型，对应UInt16）
Dim u1 As UInt16 = CType(PLC.Read("DB8.DBW0"), UInt16)

' 读取DB7.DBX0.0（位类型，对应Boolean）
Dim bitValue As Boolean = CType(PLC.Read("DB7.DBX0.0"), Boolean)

方式二：参数化读取（更灵活）

' 读取DB8中起始地址0的1个字（UInt16）
Dim u1 As UInt16 = CType(PLC.Read(DataType.DataBlock, 8, 0, VarType.Word, 1), UInt16)

' 读取DB7中起始地址0的第0位
Dim bitValue As Boolean = CType(PLC.Read(DataType.DataBlock, 7, 0, VarType.Bit, 0), Boolean)

3. 关键注意事项 #

• 禁用优化块访问：在TIA Portal中打开目标DB块属性，取消勾选「优化的块访问」，编译后下载到PLC。
• 类型严格匹配：读取的变量类型必须与PLC中定义的类型一致（如DBW对应UInt16，DBX对应Boolean）。
• 先检查连接状态：读写操作前务必确认PLC.IsConnected为True，避免无效操作。
• 添加异常捕获：通过异常处理定位具体报错原因，示例代码：

Try
    If PLC.IsConnected Then
        ' 执行读写操作
    Else
        Console.WriteLine("PLC未连接")
    End If
Catch ex As Exception
    Console.WriteLine("操作失败: " & ex.Message)
End Try

4. 修改后的完整示例代码 #

Option Strict Off
Option Explicit On
Imports S7.Net

Imports System.Data.SqlClient
Imports Microsoft.Reporting.WinForms
Imports System.Data
Imports VB = Microsoft.VisualBasic
Imports Microsoft.VisualBasic.PowerPacks
Imports System.Xml
Imports System.Text
Imports System.IO
Imports System.Security.Cryptography
Imports System.Threading
Module PLC_InOut
    ' 全局PLC实例
    Private Shared PLC As Plc
    ' 示例控制变量
    Private test1_out As Boolean = True

    ' 初始化PLC连接
    Public Sub InitPlcConnection()
        ' 替换为你的PLC实际IP地址
        PLC = New Plc(S7ProtocolType.S1200, "192.168.0.1", 0, 1)
        Try
            PLC.Open()
            If PLC.IsConnected Then
                Console.WriteLine("PLC连接成功")
            End If
        Catch ex As Exception
            Console.WriteLine("连接失败: " & ex.Message)
        End Try
    End Sub

    Public Sub PLCInOuts()
        ' 检查连接状态
        If Not PLC?.IsConnected Then
            Console.WriteLine("PLC未连接，请先初始化连接")
            Return
        End If

        Try
            ' 读取DB8.DBW0
            Dim u1 As UInt16 = CType(PLC.Read("DB8.DBW0"), UInt16)
            Dim b1() As Byte = BitConverter.GetBytes(u1)
            Console.WriteLine("DB8.DBW0读取值: " & u1)

            ' 读取DB7.DBX0.0
            Dim db7Bit As Boolean = CType(PLC.Read("DB7.DBX0.0"), Boolean)
            Console.WriteLine("DB7.DBX0.0读取值: " & db7Bit)

            ' 写入操作示例
            If test1_out Then
                PLC.Write("DB7.DBX0.0", True)
                Console.WriteLine("已将DB7.DBX0.0设为True")
            End If
        Catch ex As Exception
            Console.WriteLine("读写操作失败: " & ex.Message)
        End Try
    End Sub
End Module

内容的提问来源于stack exchange，提问作者Colatra93