VB.NET communicate problem with Mitsubishi QJ71E71

hi,all.
now i need to develop one VB.net program to send data to Q series CPU following MC 3E protocol.and now,I can connected to E71 module successful,but while i tried to send data to PLC side,program response code is ok,but PLC side cant received any data.
can anybody give me some advise?
My VB code as followingPC -> PLC,ASCII code)
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Private Sub Command1_Click(ByVal eventSender As System.Object, ByVal eventArgs As System.EventArgs) Handles Command1.Click

'Connect to the Ethernet interfece module.

Ajsock = sock

Dim ip As IPAddress = Dns.Resolve("192.0.1.253").AddressList(0)

Dim ipend As IPEndPoint = New IPEndPoint(ip, "8192")



Me.Ajsock.Connect(ipend)

MsgBox("Connection Completed")

State = Me.Ajsock.Connected()



End Sub
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Private Sub Command2_Click(ByVal eventSender As System.Object, ByVal eventArgs As System.EventArgs) Handles Command2.Click

Dim SData As Byte()

Dim RData(256) As Byte





'Send D4001 to D4003 (3 points) with the QnA-compatible 3E frame command.

'SData = Encoding.ASCII.GetBytes("500000FF03FF000018000A14010000D*004001199512021130")

'Send the data.

Me.Ajsock.Send(SData)

MsgBox("Send completion", MsgBoxStyle.Information)



'Read the response from the PLC CPU.

Me.Ajsock.Receive(RData)

MsgBox(Encoding.ASCII.GetString(RData), MsgBoxStyle.Information)



End Sub

Have you tried a packet sniffer like Ethereal to make sure the data is going out and seeing if the PLC responds?

yes I have tried to capture tcp data by ethereal.

PC ->PLC PDU as:

PLC -> PC PDU as:

In this case I changed send message asC only send 1995(HEX) to D4000.

I haven't worked with Mitsubishi's protocol. Where can I get the manual on the protocol?

you can search it at http://www.nagoya.melco.co.jp/english/.
<Q Corresponding MELSEC Communication Protocol Reference Manual>

Help me to know whether the Mitsubishi Q series E71 protocol (MC 1E/3E) is synchronous (waits until the responce comes) or asynchronous protocol (sends all request and collect all responces asynchronously)?