Communication in OMRON E5EK Digital Controller Using VB .NET

[Au123 0]

 I have a program that sends and receives data from pc to OMRON E5EK digital controller (I am using VB .NET), and I have a problem in receiving data from the controller. I suppose that I wrote the correct command, and yet it gives '??' response, when the correct one should give @ character at the beginning of the response and end with CR (Carriage Return). 

Here is my program:

Public Class Form1
    Dim TX, RXD, FCS As String

    Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
        MSComm1.Settings = "9600,E,7,2"
        MSComm1.CommPort = 4
        MSComm1.PortOpen = True
    End Sub

    Private Sub Timer1_Tick(sender As Object, e As EventArgs) Handles Timer1.Tick
        TX = "@001000000"

        Call GetFCS()
        txtRequest.Text = TX + FCS + "*"
        Call communicate()

        txtResponse.Text = RXD
    End Sub

    Private Sub GetFCS()
        Dim L As Integer
        Dim A As String
        Dim TJ As String
        L = Len(TX)
        A = 0
        For J = 1 To L
            TJ = Mid(TX, J, 1)
            A = Asc(TJ) Xor A
        Next J
        FCS = Hex(A)
        If Len(FCS) = 1 Then FCS = "0" + FCS
    End Sub

    Private Sub communicate()
        Try
            RXD = ""

            MSComm1.Output = TX

            RXD = MSComm1.Input

        Catch ex As Exception
            RXD = "Communication Error"
        End Try
    End Sub
End Class

 

Can anybody help me to fix this problem? Thank you!