Private Sub Combo5_Click()
   Select Case Combo5.Text
     Case "On"
        Instruction = &H11
     Case "Off"
        Instruction = &H10
   End Select
End Sub

Private Sub Command1_Click()
   Dim OutByte(0 To 32) As Byte
   Dim Num As Double
   Dim Num2 As String
   Dim L
   Dim Lenth2 As String
   Dim ByteXor As Byte
   Dim StrXor As String
  
   ReadPlc = True
   If Text1.Text = "" Then
     MsgBox "请输入寄存器地址", vbOKOnly, "系统提示"
   Else
     Num = Val(Text1.Text)
     Num2 = Hex(Num)
     Lenth2 = Hex(Lenth)
     ByteXor = 0
    
     OutByte(0) = 103           '起始字符
     OutByte(1) = 5             '读写指令
     OutByte(2) = Asc(0)        'PLC站地址
     OutByte(3) = Asc(2)
     OutByte(4) = Asc(Mid(Address_R, 1, 1))    '寄存器类型
     OutByte(5) = Asc(Mid(Address_R, 2, 1))
     OutByte(6) = Asc(Mid(Address_R, 3, 1))
     OutByte(7) = Asc(Mid(Address_R, 4, 1))
    
     L = Len(Num2)                          '寄存器地址
     For i = 0 To L - 1
       OutByte(11 - i) = Asc(Mid(Num2, L - i, 1))
     Next i
     For i = 0 To 3 - L
       OutByte(11 - L - i) = Asc(0)
     Next i
    
     L = Len(Lenth2)                      '读取字节数
     If L = 2 Then
       OutByte(12) = Asc(Mid(Lenth2, 1, 1))
       OutByte(13) = Asc(Mid(Lenth2, 2, 1))
     Else
       OutByte(12) = Asc(0)
       OutByte(13) = Asc(Mid(Lenth2, 1, 1))
     End If
    
     For i = 1 To 29                        'BCC校验码计算
       ByteXor = ByteXor Xor OutByte(i)
     Next i
     StrXor = Hex(ByteXor)
     If Len(StrXor) = 2 Then
       OutByte(30) = Asc(Mid(StrXor, 1, 1))
       OutByte(31) = Asc(Mid(StrXor, 2, 1))
     Else
       OutByte(30) = Asc(0)
       OutByte(31) = Asc(Mid(StrXor, 1, 1))
     End If
     OutByte(32) = 71
   End If
   MSComm1.Output = OutByte
End Sub


Private Sub Command2_Click()
Dim OutByte(0 To 32) As Byte
   Dim Num As Double
   Dim Num2 As String
   Dim L
   Dim Lenth2 As String
   Dim ByteXor As Byte
   Dim StrXor As String
   Dim Data_Send  As Double
   Dim Data_Send2 As String
   Dim SetLenth2 As String
  
   Read = False
   If Text2.Text = "" Then
     MsgBox "请输入寄存器地址", vbOKOnly, "系统提示"
   Else
     Num = Val(Text2.Text)
     Num2 = Hex(Num)
    
     SetLenth2 = Hex(SetLenth * 2)
    
     Data_Send = Val(Text4.Text)
     Data_Send2 = Hex(Data_Send)
      
     ByteXor = 0
    
     OutByte(0) = 103           '起始字符
     OutByte(1) = 6             '指令写
     OutByte(2) = Asc(0)        'PLC站地址
     OutByte(3) = Asc(2)
     OutByte(4) = Asc(Mid(Address_W, 1, 1))      '寄存器类型
     OutByte(5) = Asc(Mid(Address_W, 2, 1))
     OutByte(6) = Asc(Mid(Address_W, 3, 1))
     OutByte(7) = Asc(Mid(Address_W, 4, 1))
    
     L = Len(Num2)                             '寄存器地址
     For i = 0 To L - 1
       OutByte(11 - i) = Asc(Mid(Num2, L - i, 1))
     Next i
     For i = 0 To 3 - L
       OutByte(11 - L - i) = Asc(0)
     Next i
    
     L = Len(SetLenth2)            '写入数据的长度
     If L = 2 Then
       OutByte(12) = Asc(Mid(SetLenth2, 1, 1))
       OutByte(13) = Asc(Mid(SetLenth2, 2, 1))
     Else
       OutByte(12) = Asc(0)
       OutByte(13) = Asc(Mid(SetLenth2, 1, 1))
     End If
     '写入PLC的数据
     L = Len(Data_Send2)
     For i = 1 To L
       OutByte(14 + 2 * SetLenth - i) = Asc(Mid(Data_Send2, L - i + 1, 1))
     Next i
     For i = 1 To SetLenth * 2 - L
       OutByte(13 + i) = Asc(0)
     Next i
    
    
    
    
     '写入PLC的数据
     For i = 1 To 29                     'BCC校验码计算
       ByteXor = ByteXor Xor OutByte(i)
     Next i
     StrXor = Hex(ByteXor)
     If Len(StrXor) = 2 Then
       OutByte(30) = Asc(Mid(StrXor, 1, 1))
       OutByte(31) = Asc(Mid(StrXor, 2, 1))
     Else
       OutByte(30) = Asc(0)
       OutByte(31) = Asc(Mid(StrXor, 1, 1))
     End If
     OutByte(32) = 71
   End If
   MSComm1.Output = OutByte
End Sub

Private Sub Command3_Click()
   Dim OutByte(0 To 32) As Byte
   Dim Num As Double
   Dim Num2 As String
   Dim L
   Dim Lenth2 As String
   Dim ByteXor As Byte
   Dim StrXor As String
  
   ReadPlc = False
   If Text6.Text = "" Then
     MsgBox "请输入寄存器地址", vbOKOnly, "系统提示"
   Else
     Num = Val(Text6.Text)
     Num2 = Hex(Num)
     Lenth2 = Hex(Lenth)
     ByteXor = 0
    
     OutByte(0) = 103                         '起始字符
     OutByte(1) = Instruction                 '读写指令
     OutByte(2) = Asc(0)                      'PLC站地址
     OutByte(3) = Asc(2)
     OutByte(4) = Asc(Mid(Address_B, 1, 1))     '寄存器类型
     OutByte(5) = Asc(Mid(Address_B, 2, 1))
     OutByte(6) = Asc(Mid(Address_B, 3, 1))
     OutByte(7) = Asc(Mid(Address_B, 4, 1))
    
     L = Len(Num2)                           '寄存器地址
     For i = 0 To L - 1
       OutByte(11 - i) = Asc(Mid(Num2, L - i, 1))
     Next i
     For i = 0 To 3 - L
       OutByte(11 - L - i) = Asc(0)
     Next i
    
                                             '位地址
    
       OutByte(12) = Asc(Mid(Bit, 1, 1))
       OutByte(13) = Asc(Mid(Bit, 2, 1))
    

    
     For i = 1 To 29                        'BCC校验码计算
       ByteXor = ByteXor Xor OutByte(i)
     Next i
     StrXor = Hex(ByteXor)
     If Len(StrXor) = 2 Then
       OutByte(30) = Asc(Mid(StrXor, 1, 1))
       OutByte(31) = Asc(Mid(StrXor, 2, 1))
     Else
       OutByte(30) = Asc(0)
       OutByte(31) = Asc(Mid(StrXor, 1, 1))
     End If
     OutByte(32) = 71
   End If
   MSComm1.Output = OutByte
End Sub

Private Sub Form_Load()
   Instruction = &H11
   Address_R = "0100"
   Address_W = "0100"
   Address_B = "0100"
   Bit = "00"
   Lenth = 2
   SetLenth = 2
   MSComm1.CommPort = 1
   MSComm1.Settings = "9600,n,8,1"
   MSComm1.PortOpen = True
    If (Err) Then
       MsgBox "端口打开错误", vbOKOnly, "系统信息"
    End If
   MSComm1.RThreshold = 20
   MSComm1.InputMode = 1
   MSComm1.InBufferCount = 0
End Sub



Private Sub MSComm1_OnComm()
  Dim Temp() As Byte
  Dim Read(0 To 32) As Byte
  Dim BBC As Byte
  Dim XorByte As Byte
  Dim BBC_Temp As Byte
  Dim Value As Double
  Dim Trans(1 To 8) As Byte
  Dim TransValue As Double
  
  Value = 0
  XorByte = 0
  Temp = MSComm1.Input
  If ReadPlc = True Then
  
  If Temp(LBound(Temp)) = 103 And Temp(LBound(Temp) + 1) = 1 Then         '如果起始正确
      
      For i = 0 To 20
        Read(i) = Temp(i)
      Next i
      
      For i = 2 To 17                     '计算校验码
         XorByte = XorByte Xor Read(i)
      Next i
      
      For i = 2 To 19
        If Read(i) > &H40 Then
           Read(i) = Read(i) - &H37
        Else
           Read(i) = Read(i) - &H30
        End If
      Next
      BBC_Temp = Read(19) + Read(18) * &H10
      If XorByte = BBC_Temp Then
      
        For i = 2 To Lenth * 2 + 1
          
          Value = Value * &H10 + Read(i)
        Next i
      Text3.Text = Value
      End If
  End If
  Else
     If Temp(0) = 103 And Temp(1) = 2 Then
       MsgBox "参数设定成功", vbOKOnly, "系统提示"
     End If
  End If
End Sub


尤其是这几句，希望能具体解释一下，多谢


OutByte(0) = 103           '起始字符
     OutByte(1) = 5             '读写指令
     OutByte(2) = Asc(0)        'PLC站地址
     OutByte(3) = Asc(2)
     OutByte(4) = Asc(Mid(Address_R, 1, 1))    '寄存器类型
     OutByte(5) = Asc(Mid(Address_R, 2, 1))
     OutByte(6) = Asc(Mid(Address_R, 3, 1))
     OutByte(7) = Asc(Mid(Address_R, 4, 1))
    
     L = Len(Num2)                          '寄存器地址
     For i = 0 To L - 1
       OutByte(11 - i) = Asc(Mid(Num2, L - i, 1))
     Next i
     For i = 0 To 3 - L
       OutByte(11 - L - i) = Asc(0)
     Next i
    
     L = Len(Lenth2)                      '读取字节数
     If L = 2 Then
       OutByte(12) = Asc(Mid(Lenth2, 1, 1))
       OutByte(13) = Asc(Mid(Lenth2, 2, 1))
     Else
       OutByte(12) = Asc(0)
       OutByte(13) = Asc(Mid(Lenth2, 1, 1))
     End If
    
     For i = 1 To 29                        'BCC校验码计算
       ByteXor = ByteXor Xor OutByte(i)
     Next i
     StrXor = Hex(ByteXor)
     If Len(StrXor) = 2 Then
       OutByte(30) = Asc(Mid(StrXor, 1, 1))
       OutByte(31) = Asc(Mid(StrXor, 2, 1))
     Else
       OutByte(30) = Asc(0)
       OutByte(31) = Asc(Mid(StrXor, 1, 1))
     End If
     OutByte(32) = 71
   End If
   MSComm1.Output = OutByte
End Sub


Private Sub Command2_Click()
Dim OutByte(0 To 32) As Byte
   Dim Num As Double
   Dim Num2 As String
   Dim L
   Dim Lenth2 As String
   Dim ByteXor As Byte
   Dim StrXor As String
   Dim Data_Send  As Double
   Dim Data_Send2 As String
   Dim SetLenth2 As String
  
   Read = False
   If Text2.Text = "" Then
     MsgBox "请输入寄存器地址", vbOKOnly, "系统提示"
   Else
     Num = Val(Text2.Text)
     Num2 = Hex(Num)
    
     SetLenth2 = Hex(SetLenth * 2)
    
     Data_Send = Val(Text4.Text)
     Data_Send2 = Hex(Data_Send)
      
     ByteXor = 0
    
     OutByte(0) = 103           '起始字符
     OutByte(1) = 6             '指令写
     OutByte(2) = Asc(0)        'PLC站地址
     OutByte(3) = Asc(2)
     OutByte(4) = Asc(Mid(Address_W, 1, 1))      '寄存器类型
     OutByte(5) = Asc(Mid(Address_W, 2, 1))
     OutByte(6) = Asc(Mid(Address_W, 3, 1))
     OutByte(7) = Asc(Mid(Address_W, 4, 1))
    
     L = Len(Num2)                             '寄存器地址
     For i = 0 To L - 1
       OutByte(11 - i) = Asc(Mid(Num2, L - i, 1))
     Next i
     For i = 0 To 3 - L
       OutByte(11 - L - i) = Asc(0)
     Next i
    
     L = Len(SetLenth2)            '写入数据的长度
     If L = 2 Then
       OutByte(12) = Asc(Mid(SetLenth2, 1, 1))
       OutByte(13) = Asc(Mid(SetLenth2, 2, 1))
     Else
       OutByte(12) = Asc(0)
       OutByte(13) = Asc(Mid(SetLenth2, 1, 1))
     End If
     '写入PLC的数据
     L = Len(Data_Send2)
     For i = 1 To L
       OutByte(14 + 2 * SetLenth - i) = Asc(Mid(Data_Send2, L - i + 1, 1))
     Next i
     For i = 1 To SetLenth * 2 - L
       OutByte(13 + i) = Asc(0)
     Next i