Serialport readbyte not getting the right data

Question

I'm writing a software in VB.net to communicate with an external device with modbus I have a problem while reading data received from the device , to put it in example , using sp1.ReadByte() the data sent from the device is this :

05-03-04-00-00-01-9F-FE-0B

Update : to read data i used this code

Dim reponse As Byte() = New Byte(5 + (2 * nombre_registrre - 1)) {}

        For i As Integer = 0 To response.Length - 1

         response(i) = CByte(genvision.sp1.ReadByte())

        Next

but receive this

05-03-04-01-9F-FE-0B

I want to read it byte by byte even those 00 00 ,

Thank you so much for your help

Can you try different inputs-outputs and tell us what you get? I personally don't think that the problem is with `00` bytes as you might think — chouaib, Jan 30 '15 at 08:54
I tried many times with differents Input-output , the same thing the readbyte function seems to ignore 00 : for example now im trying with : 05-03-04-00-3A-00-0E-1E-3A and I'm receiving this : 05-03-04-3A-0E-1E-3A — dxtr, Jan 30 '15 at 09:05
How can you be sure that the device is actually sending '00' bytes? Have you tried with any other RS232 terminal to check if it's not a device issue? — Jamby, Jan 30 '15 at 10:40
@Jamby I'm tried also some Modbus simulator , and I get the same result , I can't read the 00 Byte is it normal , is this how readbyte works ? — dxtr, Jan 30 '15 at 15:19
@Jamby Using advanced serial port monitor , Im sending Hex string manually , Only NOT &H00 can be read — dxtr, Jan 30 '15 at 15:36

score 1 · Answer 1 · answered Jan 30 '15 at 07:04

1

Try :

private void serialPort1_DataReceived(object sender, SerialDataReceivedEventArgs e)
{
  byte[] array = new byte[256];
  int i = 0;
  while (serialPort1.BytesToRead > 0)
  {
    array[i]=serialPort1.ReadByte();
    i++;
  }
}

EDIT Sorry I was driven here by the C# tag! you have to be more exact next times, P.S I'm not sure how to make it in VB but it shouldn't be much different

answered Jan 30 '15 at 07:04

chouaib

2,763
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Hey , Its okey , I converted your code to VB.net and tested it , but it gives me the same result , – dxtr Jan 30 '15 at 07:43
`array[i]=serialPort1.ReadByte();` will give a compile exception `cannot implicitly convert int to byte` - see https://stackoverflow.com/questions/1318933/c-sharp-int-to-byte for conversion – Jimbo Dec 11 '19 at 05:53

score 1 · Accepted Answer · answered Jan 31 '15 at 05:07

1

Problem solved , The problem was : sp1.DiscardNull = true ,

https://msdn.microsoft.com/en-us/library/system.io.ports.serialport.discardnull(v=vs.110).aspx

thank you so much for your help

answered Jan 31 '15 at 05:07

dxtr

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Serialport readbyte not getting the right data

2 Answers2