First, you don't have to have two separate sessions for Write and Read. Some session attributes are "Local Attributes" that are managed per session, thereby you may have to set the same attributes twice for two sessions for each. Instead, having only one session simplies them.
Here's a VISA-COM C# example that just queries *IDN? response to an SCPI instrument, with 19200/N/8/1 and X-Flow. (You may change serial communication conditions according to your actual instrument to connect.)
IResourceManager rm = null;
IMessage session = null;
string strRd;
System.Array block;
try
{
rm = new ResourceManager();
session = (IMessage)rm.Open("ASRL3::INSTR", AccessMode.NO_LOCK, 0, "");
ISerial ser = (ISerial)session;
ser.BaudRate = 19200;
ser.DataBits = 8;
ser.StopBits = SerialStopBits.ASRL_STOP_ONE;
ser.Parity = SerialParity.ASRL_PAR_NONE;
ser.FlowControl = SerialFlowControl.ASRL_FLOW_XON_XOFF;
// Read until LF(0x0A) byte for *IDN? response
session.WriteString( "*IDN?\n");
strRd = session.ReadString( 100);
// Read exactly 8 bytes for *IDN? response
// (with waiting for 8 bytes get available for read)
session.TerminationCharacterEnabled = false;
session.WriteString( "*IDN?\n");
while( ser.BytesAvailable < 😎
{
;
}
block = session.Read( 8);
}
catch( System.Runtime.InteropServices.COMException ex)
{
MessageBox.Show( ex.Message, "error 0x" + Convert.ToString(ex.ErrorCode, 16));
}
finally
{
session.Close();
}
In the TRY block, there are two different approaches for reading, 1)typical ASCII read until LF(0x0A) terminate, 2)block read for specific byte length. As for typical ASCII command IO bases, the 1st approcah is much easier. As for arbitrary block read, you should disable the TerminationCharacterEnabled property to avoid unexpected termination for the case when an LF code was encountered. Also you can check the byte length that is available in the read-buffer by using ISerial.BytesAvailable property before reading.
Hope this helps.
Makoto Kondo
