Read Data From serial Port, but data received is coded as displays series of squares

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Dear Friends

I am writing a program in VB.NET 2010 to read data from a device through rs232 port

VB

btnStart.Enabled = False
btnStop.Enabled = True
If SerialPort1.IsOpen Then SerialPort1.Close()
SerialPort1.PortName = cmbPorts.Text
SerialPort1.BaudRate = cmbBaudRate.Text
SerialPort1.Parity = IO.Ports.Parity.None
SerialPort1.StopBits =  IO.Ports.StopBits.One
SerialPort1.DataBits =  8
SerialPort1.Encoding =  System.Text.Encoding.Unicode
SerialPort1.ReadBufferSize = 4096
SerialPort1.Open()

then I have written to read the data as follows

VB

'Declared this delegate at top of form
Delegate Sub SetTextCallback(ByVal [text] As String) 

Private Sub SerialPort1_DataReceived(sender As Object, e As System.IO.Ports.SerialDataReceivedEventArgs) Handles SerialPort1.DataReceived
        Try
            ReceivedText(SerialPort1.ReadExisting())    
        Catch ex As Exception
            MsgBox(ex.Message)
        End Try
    End Sub
    Private Sub ReceivedText(ByVal [text] As String)
           If Me.TextBox1.InvokeRequired Then
            Dim x As New SetTextCallback(AddressOf ReceivedText)
            Me.Invoke(x, New Object() {(text)})
        Else
            Me.TextBox1.Text &= [text]
        End If
    End Sub

Posted 5-Jul-13 4:39am

JYOTIRMOY SAMANTA

Updated 5-Jul-13 7:11am

v2

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Richard MacCutchan 5-Jul-13 10:55am

Are you sure that the device is sending you ASCII characters?

JYOTIRMOY SAMANTA 5-Jul-13 12:05pm

actually the textbox where I display the message shows a series of sqlares like □ □ □ □

Richard MacCutchan 5-Jul-13 13:08pm

But that means nothing, not all bytes are printable characters, and what you receive may still be valid data. You need to look at the actual values of each byte received and compare it with the expected response.

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OriginalGriff · Answer 1 · 2013-07-05T05:17:00

Solution 1

The changes are that the data you are receiving is not straight characters, but binary values. This may be because the device you are connected to is not sending string data but binary values, or it could be because your port configuration is incorrect: baud rate, bits per character, or parity for example.

Try reading the data from the port as bytes, and displaying the hex values:

C#

Dim i As Integer = SerialPort1.BytesToRead
Dim data As Byte() = New Byte(i - 1) {}
i = SerialPort1.Read(data, 0, i)
Dim s As String = String.Join(" ", data.[Select](Function(c) c.ToString("X02")))

That should at least give you an idea what data is being returned.

Posted 5-Jul-13 5:17am

OriginalGriff

Comments

JYOTIRMOY SAMANTA 5-Jul-13 11:54am

How to determine which settings should I apply? or how to find which configuration is suitable or correct.

OriginalGriff 5-Jul-13 11:58am

Best thing to do is look at the documentation! There are standard speeds you can try: 9600, 19200, and so forth, but it could take forever to "guess" the right settings, and even then you might get it slightly wrong and it fails in the future (for example, baud rates have a tolerance of 10%, so if you are "close" it may work with the specific unit and PC you have there, but fail completely on a different unit).

Talk to the manufacturers! It is by far the easiest way :laugh:

JYOTIRMOY SAMANTA 5-Jul-13 12:21pm

Actually I have checked the Device Manager and checked the COM1 port setting it was same as my settings and software supplied by the vendor of that device is showing correct data. but when try with my code it gives error. a series of squares

The device is EM-100 Chemistry Analyzer

OriginalGriff 5-Jul-13 14:01pm

Any setting sin the Device Manager does not reflect the settings as required by the device *at the other end* - it will just show the current or default settings. There is nothing stopping the manufacturers software changing that when (and only when) it want to talk. What did the manufacturers of the device say it wanted, and what it outputs?

SoMad 5-Jul-13 18:26pm

As Richard and OriginalGriff have already said, even though you only see 'squares', that does not mean it is an error. You are seeing the data in this way because the values cannot be displayed as characters on the screen. As OriginalGriff said, you will most likely have to contact the manufacturer to figure out how the data is formatted.
In the software supplied by the manufacturer, are you able to see which COM port settings it is using (in a setup screen within the program)?

Soren Madsen

JYOTIRMOY SAMANTA 10-Jul-13 2:17am

Encoding is ASTM E1381 – 02

JYOTIRMOY SAMANTA 5-Jul-13 21:23pm

Is there any tools which I can use to determine the perfect settings for my RS232 DEVICE
or I have to trial and Error if i failed to get help from the vendor.
How to determine the TextEncoding like UTF-8, ASCII, UTF-7, UNICODE and BAUD RATE.

OriginalGriff 6-Jul-13 4:09am

No, not really. There are hadrware device that can examine incomming data and determine the baud rate and so forth for you (called Protocol Analysers - I have one) but they are seriously expensive pieces of kit (mine was around £5000) and probably overkill for what you want.
The chances are that the manufacturers publish the information complete with the data format - most do - or that their tech support will have it to hand. Unless of course you are trying to reverse engineer their hardware to produce your own version! :laugh: They may not be so helpful then...

JYOTIRMOY SAMANTA 6-Jul-13 11:30am

Dear Friends thanks all

I have now one more Information to give you that the device Is using ASTM Protocol
I think that may be the reason that I was getting such output.
Can anyone help me to connect and read the data from a Device with RS232C interface and
ASTM PROTOCOL

OriginalGriff 6-Jul-13 11:36am

Hmmm. Which one?
There are loads...
https://www.google.co.uk/search?q=ASTM+PROTOCOL&oq=ASTM+PROTOCOL&aqs=chrome.0.57&sourceid=chrome&ie=UTF-8
http://en.wikipedia.org/wiki/ASTM_International

JYOTIRMOY SAMANTA 10-Jul-13 2:11am

it is ASTM E1381 – 02

OriginalGriff 10-Jul-13 3:35am

Then the first thing to do is look at teh definition of the comms standard:
http://www.astm.org/Standards/E1381.htm
(It's superseded, but it's possible you are interfacing to older equipment)
Then I'm afraid, you are going to have to read the whole spec, and work out what is going on. I can't write it for you - that's a proper job that would mean I'd have to charge! :laugh:

JYOTIRMOY SAMANTA 6-Jul-13 11:44am

What do you want to know?