Can I query the list of variables and types

Question

Can I use twincat-ads to query a Beckhoff PLC for the variables (and their types) that are exposed on ADS.

Answer 1

Yes you can.

This example comes directly from the Beckhoff ads documentation which you should study a bit in order to understand the basics of the ads protocol.

/// <summary>
/// Defines the entry point of the application.
/// </summary>
/// <param name="args">The arguments.</param>
static void Main(string[] args)
{
    Console.WriteLine("");
    Console.WriteLine("Press [Enter] for start:");
    Console.ReadLine();

    // Parse the command-line arguments
    AmsAddress address = ArgParser.Parse(args);

    using (TcAdsClient client = new TcAdsClient())
    {
    // Connect the AdsClient to the device target.
    client.Connect(address);

    // Load symbolic information
    ISymbolLoader loader = SymbolLoaderFactory.Create(client, SymbolLoaderSettings.Default);
    ReadOnlySymbolCollection allSymbols = loader.Symbols;

    ISymbol bVar1 = allSymbols["GVL.bVar1"];
    ISymbol bVar2 = allSymbols["GVL.iCount"];
    ISymbol projectName = allSymbols["TwinCAT_SystemInfoVarList._AppInfo.ProjectName"];

    SymbolCollection symbols = new SymbolCollection() {bVar1, bVar2, projectName};

    // Sum Command Read
    SumSymbolRead readCommand = new SumSymbolRead(client,symbols);
    object[] values = readCommand.Read();

    for (int i = 0; i < symbols.Count; i++)
    {
        Console.WriteLine("Symbol: {0} (Value: {1}, Type: {2})",symbols[i].InstancePath,values[i].ToString(),values[i].GetType().Name);
    }

    // Sum Command Write
    SumSymbolWrite writeCommand = new SumSymbolWrite(client,symbols);
    object[] writeValues = new object[] {true, (short) 42, "MyNewProjectName"};

    writeCommand.Write(writeValues);
    }

    Console.WriteLine("");
    Console.WriteLine("Press [Enter] for leave:");
    Console.ReadLine();
}

In C++ you need to use the AdsSyncReadReq function:

#include <iostream.h>
#include <windows.h>
#include <conio.h>
#include <assert.h>

// ADS headers for TwinCAT 3
#include "C:\TwinCAT\AdsApi\TcAdsDll\Include\TcAdsDef.h"
#include "C:\TwinCAT\AdsApi\TcAdsDll\Include\TcAdsAPI.h"

void main()
{
  long                  nErr, nPort; 
  char                  *pchSymbols = NULL; 
  UINT                  uiIndex; 
  AmsAddr               Addr; 
  PAmsAddr              pAddr = &Addr; 
  AdsSymbolUploadInfo   tAdsSymbolUploadInfo; 
  PAdsSymbolEntry       pAdsSymbolEntry; 

  // Open communication port on the ADS router
  nPort = AdsPortOpen();
  nErr = AdsGetLocalAddress(pAddr);
  if (nErr) cerr << "Error: AdsGetLocalAddress: " << nErr << '\n';

  // Select Port: TwinCAT 3 PLC1 = 851
  pAddr->port = 851;

  // Read the length of the variable declaration
  nErr = AdsSyncReadReq(pAddr, ADSIGRP_SYM_UPLOADINFO, 0x0, sizeof(tAdsSymbolUploadInfo), &tAdsSymbolUploadInfo);
  if (nErr) cerr << "Error: AdsSyncReadReq: " << nErr << '\n'; 
  pchSymbols = new char[tAdsSymbolUploadInfo.nSymSize]; 
  assert(pchSymbols); 

  // Read information about the PLC variables 
  nErr = AdsSyncReadReq(pAddr, ADSIGRP_SYM_UPLOAD, 0, tAdsSymbolUploadInfo.nSymSize, pchSymbols); 
  if (nErr) cerr << "Error: AdsSyncReadReq: " << nErr << '\n'; 

  // Output information about the PLC variables 
  pAdsSymbolEntry = (PAdsSymbolEntry)pchSymbols; 
  for (uiIndex = 0; uiIndex < tAdsSymbolUploadInfo.nSymbols; uiIndex++)
  { 
    cout << PADSSYMBOLNAME(pAdsSymbolEntry) << "\t\t" 
         << pAdsSymbolEntry->iGroup << '\t' 
         << pAdsSymbolEntry->iOffs << '\t' 
         << pAdsSymbolEntry->size << '\t' 
         << PADSSYMBOLTYPE(pAdsSymbolEntry) << '\t' 
         << PADSSYMBOLCOMMENT(pAdsSymbolEntry) << '\n'; 
    pAdsSymbolEntry = PADSNEXTSYMBOLENTRY(pAdsSymbolEntry); cout.flush();
  }
  getch();

  // Close communication port
  nErr = AdsPortClose(); 
  if (nErr) cerr << "Fehler: AdsPortClose: " << nErr << '\n';

  // Release memory
  if (pchSymbols) delete(pchSymbols);
} 

For more info:

https://infosys.beckhoff.com/english.php?content=../content/1033/tc3_ads_intro/9007199370899851.html&id=5869483416056481636