大家帮忙，看看我的VB、omron通讯程序

下面是我试编的程序，我往DM0000中写入FFFF，然后将PLC的响应显示在Text1中。运行时，程序没有报告错误，但是在Text1中没有任何反应。请大家帮忙看看。谢谢

Private Sub Command1_Click()
Dim outdata, L, fcs1, i, FCS, instring, fcs2, fcs3 As String
 outdata = "@00WD0000FFFF"
 L = Len(outdata)
 fcs1 = 0
 For i = 1 To L
   fcs1 = fcs1 Xor Asc(Mid(outdata, i, 1))
 Next i
 FCS = Hex(fcs1)
 Text1.Text = FCS
 MSComm1.Output = outdata + "FCS " + "*" + Chr$(13)
 
 Do
    DoEvents
 Loop Until MSComm1.InBufferCount >= 10
 instring = MSComm1.Input
 Text2.Text = instring
 
 fcs2 = 0
 For i = 1 To Len(instring) - 4
 fcs2 = fcs2 Xor Asc(Mid(instring, i, 1))
 Next i
 fcs3 = Hex(fcs2)
 If fcs3 = Mid(instring, Len(instring) - 3, 2) Then
  Text3.Text = "right"
 Else
  Text3.Text = "wrong"
 End If
 
End Sub

Private Sub Form_Load()
 MSComm1.CommPort = 1
 MSComm1.Settings = "9600,e,7,2"
 MSComm1.InputLen = 0
 MSComm1.PortOpen = True
End Sub

请说得详细一些。