Determining how many bytes are available to read from a visa serial port.

[Steve_Block]

In labview under visa there is a number of bytes at serial port property. How do I access this from c# if I'm using ni visa? When I use the ReadString() function it throws an exception unless I specify this number of bytes. Is there a way to call Readstring to report only what is in the buffer without having to worry about how many bytes to read?

[Tom__Sedlack]

VB uses SerialPort1.BytesToRead.   I would guess there is a C# equivalent.

[Steve_Block]

I need to use the visa serial ports because I want to make my drivers able to use any available interface on the fly.

[Curt_C]

Hi,

I don't know if this will help, but when I use a Visa Serial Session with C# I set the termimnation character property to true

and select a terminating character. In this case char 13.

Curt

private 
private int m_comport = 2;
private int m_baudrate = 19200;
private int m_timeout = 10000;SerialSession m_session;

public bool OpenSession()
        {

            try
            {

                m_session = new SerialSession("ASRL" + m_comport + "::INSTR");
                m_session.BaudRate = m_baudrate;
                m_session.StopBits = StopBitType.One;
                m_session.Parity = Parity.None;
                m_session.FlowControl = FlowControlTypes.None;
                m_session.Timeout = m_timeout;
                m_session.TerminationCharacter = 13;
                m_session.TerminationCharacterEnabled = true;
                return true;

            }
            catch (NationalInstruments.VisaNS.VisaException visaex)
            {
                Trace.WriteLine("OpenSession VisaException: " + visaex.Message);
                return false;
            }
            catch (Exception ex)
            {
                Trace.WriteLine("OpenSession Exception: " + ex.Message);
                return false;
            }
        }

//and then read it


strReceive = m_session.ReadString();

[BROhan]

Hi Steve,

Take a look at the following VISA function:

viGetAttribute (, VI_ATTR_ASRL_AVAIL_NUM, );

You may need to change the parameters accordingly, but use the NI-VISA Help as a reference (Start->All Programs->National Instruments->VISA).

[Steve_Block]

So far Brohan's response is the closest to what I'm looking for. This looks like a CVI parameter though and I need to know how to access it in C#. The other answers don't suffice because they are serial port specific and I need code that allows me to interchange protocals freely.

[BROhan]

Check out the .NET help for VISA from the same location. I found this function call:

public byte GetAttributeByte( AttributeType attribute );

You can use the AsrlAvailNum attribute.