Reply To: GPIBNI, VISA, 34401A and *OPC? failing

[Tony Goodhew]

I reimplemented this in C# using the NI VISA libraries and the code works as expected:

using Ivi.Visa;
using NationalInstruments.Visa;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Runtime.ConstrainedExecution;
using System.Text;
using System.Threading;
using System.Threading.Tasks;

namespace SRQTest
{
    internal class Program
    {
        public static GpibSession gpibSession;
        public static NationalInstruments.Visa.ResourceManager resManager;
        public static int gpibIntAddress = 14; // 34401A
        public static string gpibAddress = string.Format("GPIB0::{0}::INSTR", gpibIntAddress);
        public static SemaphoreSlim srqWait = new SemaphoreSlim(0, 1); // use a semaphore to wait for the SRQ events

        static void Main(string[] args)
        {
            // Setup the GPIB connection via the ResourceManager
            resManager = new NationalInstruments.Visa.ResourceManager();

            // Create a GPIB session for the specified address
            gpibSession = (GpibSession)resManager.Open(gpibAddress);
            gpibSession.TimeoutMilliseconds = 8000; // Set the timeout to be 4s
            gpibSession.TerminationCharacterEnabled = true;
            gpibSession.Clear(); // Clear the session

            gpibSession.ServiceRequest += SRQHandler;

            SendCommand("*RST"); // Reset the DMM
            SendCommand("*CLS"); // Clear the DMM status registers
            SendCommand("*ESE 1"); // Enable "operation complete" bit to set "standard event" bit in status byte
            SendCommand("*SRE 32"); // Enable "standard event" bit in status byte to pull the IEEE-488 SRQ line

            var opcResult = QueryString("*OPC?"); // Assure synchronization
            Console.WriteLine($"OPC Result: {opcResult}"); // Print the result of the OPC query

            SendCommand("CONF:VOLT:DC 10"); // Set DMM to 10 volt DC range
            SendCommand("VOLT:DC:NPLC 10"); // Set the integration time to 10 PLCs
            SendCommand("TRIG:COUN 100"); // DMM will accept 100 triggers
            SendCommand("INIT"); // Place DMM in "wait-for-trigger" state
            SendCommand("*OPC"); // Set "operation complete" bit in standard event
            // Wait for the SRQ event
            srqWait.Wait(); // Wait for the SRQ event to be signaled
            // Read the data
            string response = QueryString("FETCH?");
            Console.WriteLine($"1. Response: {response}");
            // Clear the DMM status registers
            SendCommand("*CLS");
        }

        public static void SRQHandler(object sender, Ivi.Visa.VisaEventArgs e)
        {
            // Read the Status Byte
            var gbs = (GpibSession)sender;

            StatusByteFlags sb = gbs.ReadStatusByte();
            Console.WriteLine($"1. SRQHandler - Status Byte: {sb}");

            gpibSession.DiscardEvents(EventType.ServiceRequest);

            SendCommand("*CLS");

            srqWait.Release();
        }

        static private void SendCommand(string command)
        {
            gpibSession.FormattedIO.WriteLine(command);
        }

        static private string ReadResponse()
        {
            return gpibSession.FormattedIO.ReadLine();
        }

        static private string QueryString(string command)
        {
            SendCommand(command);
            return (ReadResponse());
        }
    }
}

Looking at the NI IO Trace Utility, I can see that the HTBasic program differs in that it doesn’t add a 0A to the end of the *OPC? string – Adding END to the OUTPUT statement fixes that and I can continue on but I now run into a problem on line 270 with HT Basic giving an Error 170 “I/O operation not allowed”:

270 ENABLE INTR Hpib;Mask ! Enable SRQ to interrupt the program

If I swap to the GPIBNI driver then the program works successfully.

TonyG