Android Question Cannot write specific sequence of byte to serial port

Discussion in 'Android Questions' started by fabton1963, Feb 19, 2015.

  1. fabton1963

    fabton1963 Member Licensed User

    Hi ,
    I'm writing a code that use serial port comunication.
    I' need to write a specific sequence byte to serial port to initialize the attached device.

    in hex
    28 02 AF E7 FF 00 C1
    40 2 175 231 255 0 193

    In classic VB I may use the followin code:

    With MSComm1
    .Settings = "9600,n,8,1"
    .InputMode = comInputModeBinary
    End With
    MSComm1.PortOpen = True
    Dim Buffer As String

    Buffer = Chr("&h28") & Chr("&h02") & Chr("&hAF") & Chr("&hE7") & Chr("&hFF") & Chr("&h00") & Chr("&hC1")
    MSComm1.Output = Buffer

    Using b4j or b4a I try using Astream object writing byte sequence
    dim b() as byte
    b(0) = 40
    b(1) = 1
    b(2) = 126
    b(3) = 10
    b(4) = 1
    b(5) = 7
    astream.Write( b)

    works !!

    b(0) = 40
    b(1) = 1
    b(2) = 234
    b(3) = 228
    b(4) = 1
    b(5) = 7
    astream.Write( b)

    does not works !!!

    I also try sendig word instead of byte with following code with no result !!

    dim b(6) as string
    Dim bc As ByteConverter
    dim J as int

    b(0) = "40"
    b(1) = "2"
    b(2) = "175"
    b(3) = "231"
    b(4) = "127"
    b(5) = "0"
    b(6) = "193"

    For J = 0 To 6
    Dim I As Short = data(J)
    Dim bytes() As Byte = bc.ShortsToBytes(Array As Short(I))
    If astream.Write( bytes) Then
    ' ...
    ' ...
    End If
    Log("error ...")
    End Try

    Please help me.
  2. Troberg

    Troberg Well-Known Member Licensed User

    My guess: Byte numbers larger than 127 becomes negative numbers, and there, somewhere, things go bad. B4A uses signed bytes.

    As for the last example, call me stupid, but I don't see how you go from b() to what you send. You fill b(), then you don't use it anymore.

    I would probably just use more or less the VB variant and convert it to string, one character at the time, then send the string.
  3. Erel

    Erel Administrator Staff Member Licensed User

    It doesn't matter that that the bytes are signed. The correct value will be sent.

    The problem is somewhere else.

    You can write it like this:
    'Chr("&h28") & Chr("&h02") & Chr("&hAF") & Chr("&hE7") & Chr("&hFF") & Chr("&h00") & Chr("&hC1")
    AStream.Write(Array As Byte(0x280x020xAF0xE70xFF0x000xC1))
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