基于MODBUS协议和PLC的通讯

很多人在找MODBUS通讯代码，我把以前用VB.NET写的一些代码贴上来供参考

'判断电机是否在转动
    Public Sub WaitMotorStop()
        '判断电机是否在转动
        Dim str1 As String = "1"
        Do Until str1 = "0"
            Comm2PLC(RCS, Relay901, "")
            System.Threading.Thread.Sleep(50)
            Dim str2 As String = FormMain.RS232.ReadExisting().ToString()
            FormMain.RS232.DiscardInBuffer()
            FormMain.RS232.DiscardOutBuffer()
            '先高低位转换，再16进制转换为10进制。例如把78563412转换为12345678
            If str2.Length > 6 Then
                str1 = str2.Substring(6, 1)
            End If
        Loop
        Thread.Sleep(200)
    End Sub
    ‘----------------------------------------------------------------’
    '写入PLC
    Public Sub Comm2PLC(ByRef _Code As String, ByRef _Address As String, ByVal _Command As String)
        Dim str1 As String = _Code & _Address & _Command         '代码字+中间继电器+命令字
        Dim str2 As String = Calculte_Vertification_bit(str1)
        Dim str3 As String =