Char displayed as 'boxes' in textbox?!

[nescartel]

Hello everyone,

New forum member here. had this weird problem, and can't seem to find the solution anywhere! I am using VB .net 2005 on an XP based laptop. I have this controller-based hardware connected to the serial port of my laptop. My serial port is only using 3 pins, transmit, receive, and signal ground. I am transmitting hexadecimal bytes contained in an array to the hardware and expects to get response from the hardware.

If let's say I transmit 15, 4, 17, 6, (in hexadecimal) sequentially; the hardware will execute 'system reset'. I managed to do this just fine by using;

TxBuffer = New String() {Chr(&H15), Chr(&H4), Chr(&H17), Chr(&H6)}

the hardware DID reset on this event , but if I want to monitor the data sent through serial port by putting the transmitted data in a textbox as below;

TextBox1.Text = TextBox1.Text & " " & TxBuffer(i)

instead of the "15, 4, 17, 6" that I transmitted, the textbox just displays 4 'boxes'! i tried editing the transmitted data by deleting the 'char' typecast from the above code, turning it into;

TxBuffer = New String() {&H15, &H4, &H17, &H6}

by using this, i can display the transmitted data in textbox very well, but the hardware did not reset . why is this so? i want the user to be able to display the transmitted text correctly, how can i do this?

here is my complete code. it is very short, resides on only 1 form that has one textbox to display the transmitted data, and one button to trigger the transmission of data to serial port. please advise, thank you!

Public Class Form1

    Dim TxBuffer() As String    'Telegram message to send
    Dim TxBufferSize As Integer 'Size of dynamic array

    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        SerialPort1.Open()
    End Sub

    Private Sub Form1_FormClosed(ByVal sender As Object, ByVal e As System.Windows.Forms.FormClosedEventArgs) Handles Me.FormClosed
        SerialPort1.Close()
    End Sub

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        TxBuffer = New String() {Chr(&H15), Chr(&H4), Chr(&H17), Chr(&H6)} 'reset OK, but display squares
        'TxBuffer = New String() {&H15, &H4, &H17, &H6}                     'reset not OK , but display OK

        TxBufferSize = UBound(TxBuffer) 'Get array size
        TransmitData(TxBuffer,TxBufferSize)
    End Sub


End Class

 

[cjard]

instead of the "15, 4, 17, 6" that I transmitted

erm.. no, you didnt transmit "15, 4, 17, 6" because that, in hex, is:

&H22 &H31 &H35 &H20 &H2C &H20 &H34 &H2C &H20 &H31 &H37 &H2C &H20 &H36 &H22

A character of hex code 4, is not the numerical digit "4". "4" is &H34, or 52 in decimal

Chr(52) = "4"

Now, can you see why your textbox shows just control characters (boxes) ?

 

[nescartel]

hurmm... i'm still confused here...
the thing is, the code;

TxBuffer = New String() {Chr(&H15), Chr(&H4), Chr(&H17), Chr(&H6)}

is doing exactly the right thing as i wanted,
but somehow i cannot display it in textbox.
why is it displaying squares instead of the data as above?
what is it that i did not understand?
would you be so kind as to point it out for me?

thank you in advance...

 

[cjard]

the character A is 65 is decimal, or &H41 in hex


This means:

TxBuffer = New String() {Chr(&H41), Chr(&H41), Chr(&H41), Chr(&H41)}

When shown in a text box, will be AAAA


The hex number 15, when converted to a character IS NOT the string "15". Chr(&H15) IS NOT A PRINTABLE CHARACTER


I dont know how else to explain this to you: An array of 4 characters that are not printable is NOT THE SAME THING as a string of "15, 4, 7, 6"

Look at this table:

Those are the ascii codes for characters.. If you have a number, 65, (&H41) and you convert it to a character, it becomes A
If you have a number, 21 (&H15) and you convert it to a character, it becoems NAK (according to that table, an ascii control character probably) IT DOESNT BECOME A STRING OF THE CHARACTER "1" (which is character Chr(&H31) ) followed by "5" (which is character code Chr(&H35) )

I cant really think of any other way I can put this.. You cant convert a byte array (what youre sending to the device) directly to a string, and turn all the bytes within, into a numerical representation, because there isnt a mapping like that

If you want to convert byte &H4E into the string "4E" then you have to call .ToString("X") on it. Trying to convert it into a char will result in it becoming the character "N" because N's number in the ascii table is 4E

 

[nescartel]

owh, now i get it!
no wonder it's displaying boxes,
those are actually NOT ACKNOWLEDGE, END OF TRANSMISSION, etc,
all are non printed characters!

thank you for your generous explanation cjard!
found a workaround for that problem,
instead of transmitting the data and try to display the ascii data,
i split the data into 2 behavior,
one to be displayed on textbox,
and another one to be converted into ascii and transmitted.

thank you so much!