VB.net, reading into 2 bytes from instrument, how do I separate them?

Recon

I'm using VB.net to take a reading from an A/D converter. Using

txtBytesToRead.Text = SerialPort.BytesToRead

I can see that there are 2 bytes there to be read. What I'm reading in is a 12 bit digital signal from the A/D.

What command can I use to see the 2 bytes? The .ReadLine method justs times out because my A/D doesn't send a carriage return and the .Read method is giving an error

"Overload resolution failed because no accessible 'Read' accepts this number of arguments"

before running the program.

Does anyone here have any experience with this?

ronkmonster

Are you trying to split the string in txtBytesToRead.Text to 2 individual parts?

Recon

not in that textbox but later in the code, I just want to try to read the data from the A/D first and take it from there. The A/D returns 2 bytes that I'll need to work with separately before combining them. I'll assign each of these bytes to two variables (MSB and LSB).

After looking through the help in Visual Studio 2005 I found

Dim instance As SerialPort
Dim buffer As Byte()
Dim offset As Integer
Dim count As Integer
Dim returnValue As Integer

returnValue = instance.Read(buffer, offset, count)

where

buffer
The byte array to write the input to.

offset
The offset in the buffer array to begin writing.

count
The number of bytes to read.

I'm getting an error from this saying that 'buffer' needs to be assigned a value but I'm not sure what Byte value to assign it!

Recon

I have a demo of a labview program which works but I need to get it going in VB.net

NeverSayDie

You probably need to initialise that Byte array to hold however many bytes you're planning on reading. You don't add Bytes to it, the Read() method will do that, but there presumably needs to be room in there for them. (I'm assuming you're setting the values for the count and offset params)

ronkmonster

Dim buffer As Byte() = New Byte(2); Have to set the size of the array before use

FSL

I have not used VB net but here is an extract from a VB6 programme which grabs data from an instrument attached to a serial port
MSComm2 is a comm control
buf is a variant and d is a byte array

Private Sub MSComm2_OnComm()

If Me.MSComm2.CommEvent = comEvReceive Then
buf = MSComm2.Input
d = buf
'

'the rest of the code assigns specific byte(s) to
'various variables
e.g. tmst = Chr(d(295)) & Chr(d(296)) & Chr(d(297)) & Chr(d(298)) & Chr(d(299))
'
'
end if

end sub

EL_Loco

so why not initialise the buffer() array with something?

it should get filled with what's been written from the instance.read function/method anyway? (which is strange because if it's going to be filled with info from your .read part, why assign it a value before hand)

Dim instance As SerialPort
Dim buffer As Byte()
Dim offset As Integer
Dim count As Integer
Dim returnValue As Integer

buffer(0) = 1; // do arrays start at 0 or 1 in VB?

// what are the values for the rest of the parametres in that statement?

offset = 0; // start reading at the beginning
count = 2; // to count 2 bytes

// all the parametres should have values before you call this next line

returnValue = instance.Read(buffer, offset, count)

// maybe check the length of your array and see how many elements in the array got filled

msgbox(ubound(buffer))

NeverSayDie

EL_Loco wrote: »

so why not initialise the buffer() array with something?

it should get filled with what's been written from the instance.read function/method anyway? (which is strange because if it's going to be filled with info from your .read part, why assign it a value before hand)

You don't have to put stuff in it beforehand, but you will have to specify what size it is - arrays in VB.NET aren't dynamic.

Recon

Thanks for all the replies so far, when I try to use

Dim buffer As Byte() = New Byte(2)

I get an error "Type 'Byte' has no constructors", but it does take away the other error I was getting!

NeverSayDie

Recon wrote: »

Thanks for all the replies so far, when I try to use

Dim buffer As Byte() = New Byte(2)

I get an error "Type 'Byte' has no constructors", but it does take away the other error I was getting!

That should probably be;
Dim buffer As Byte(2)

You can declare the array uninitialised if you want, but I don't think you can then initialise it to bounds in the same line.

EL_Loco

damn you VB arrays. hope it's working out anyway OP.

NeverSayDie

EL_Loco wrote: »

damn you VB arrays. hope it's working out anyway OP.

Well, if it's any consolation, that's how it works in C++, Java and C# as well

If you do want dynamic collections btw, the Systems.Collections namespace has lots of handy classes in it - ArrayLists, generic lists and hashtables/dictionaries, stacks, queues, etc.

Recon

Thanks again for the help, this is what the solution was...

Dim MSB As Byte
            Dim LSB As Byte

            txtBytesToRead.Text = SerialPort.BytesToRead 'just to check that there's only 2 bytes there to be read

            MSB = SerialPort.ReadByte 'all I needed to do what read a byte twice...
            LSB = SerialPort.ReadByte

            txtMSB.Text = MSB 'just to show the values while testing
            txtLSB.Text = LSB

            voltage = ((((MSB * 256) + LSB) / 4095) * 5) 'it's a 12 bit A/D

            txtVolt.Text = voltage