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<title>Delphi OPC Programming</title>
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<h1>Delphi OPC Programming</h1>
<h3>Introduction</h3>
<p>This document, and the ZIP archive of which it is part, are intended to
help give a brief introduction to OPC (formerly OLE for Process Control)
development using Borland Delphi.</p>
<p>The ZIP file contains Delphi translations of the published OPC custom
interfaces, i.e. OPC Common 1.1, Data Access 3.0 (and earlier), Alarms &
Events 1.10, Historical Data Access 1.2 and Security 1.0.</p>
<p>The code has been confirmed to be compatible with with Delphi 3 to 7, and
Delphi 2005 to 2009 for Win32.</p>
<p>The <a href="http://www.opcconnect.com/delphi.php">Delphi page</a> at OPC
Programmers' Connection also has Delphi source code for a demo OPC client
and server.</p>
<h3>Version History</h3>
<p><b>October 5th 2008:</b> Confirmed compatibility with Delphi 2009 (no code
changes).</p>
<p><b>December 11th 2003:</b> Added error codes for Complex Data 1.0. Added
OPCHDA_PARTIAL quality for HDA 1.2.</p>
<p><b>March 10th 2003:</b> Updated for Data Access 3.0.</p>
<p><b>October 31st 2002:</b> Added support for new OPC Alarms & Events
1.10 interfaces: IOPCEventServer2 and IOPCEventSubscriptionMgt2.</p>
<p><b>October 22nd 2002:</b> Added support for new OPC Common 1.1 interfaces:
IOPCServerList2 and IOPCEnumGUID.</p>
<p><b>September 13th 2002:</b> Added support for OPC Security 1.0 (unit
contributed by <a href="mailto:ikysil@ua.fm">Illya Kysil</a>).</p>
<p><b>September 6th 2002:</b> Corrected OPC_WRITABLE to OPC_WRITEABLE in
OPCDA.pas.</p>
<p><b>September 3rd 2002:</b> Minor changes for compatibility with Delphi
7.0.</p>
<p><b>August 6th 2002:</b> Updated OPCHDA.pas to correct declaration of
IOPCHDA_SyncRead.ReadAttribute (thanks to Arjan Lamaker for pointing out the
error). Also updated Internet addresses in file header comments.</p>
<p><b>July 26th 2002:</b> Updated OPCHDA.pas to explicitly declare const
CATID_OPCHDAServer10 as a TGUID.</p>
<p><b>July 22nd 2002:</b> Updated OPCDA.pas with corrected item property IDs
(200 to 207) from Data Access 2.05A specification.</p>
<p><b>July 5th 2001:</b> Confirmed compatibility with Delphi 6.0 (no code
changes).</p>
<p><b>June 20th 2001:</b> Added support for OPC Historical Data Access 1.1
(with help from <a href="mailto:ikysil@ua.fm">Illya Kysil</a>).</p>
<p><b>June 19th 2001:</b> Removed unneeded IID_IEnumString declarations.</p>
<p><b>March 7th 2001:</b> Pascal type definitions modified for all interface
input parameters which are of array types. This is to more accurately
indicate the required data. As a consequence, any client which implements the
IOPCDataCallback interface will need minor code changes.</p>
<p>Factored out common type definitions into new file OPCtypes.pas; this
should be added to the uses list of all source files which make use of OPC
interfaces. This change is needed to avoid compilation errors when using the
Data Access and Alarms & Events interfaces from the same unit.</p>
<p>Definition removed for type PWORDARRAY to prevent possible conflict with
the Delphi SysUtils unit.</p>
<p><b>October 26th 1999:</b> Extra type definitions added to OPCDA.pas, for
use with connection points.</p>
<p><b>October 12th 1999:</b> OPC interface files and sample client program
now packaged separately.</p>
<p><b>September 11th 1999:</b> Now works with Delphi 3, 4 and 5.</p>
<p><b>June 22nd 1999:</b> Original version, compatible with Delphi 4.</p>
<h3>File List</h3>
<p>Inside the ZIP archive you will find the following files.</p>
<table border="0" cellspacing="0" cellpadding="0" summary="">
<tr>
<td><b>OPCCOMN.pas</b></td>
<td width="50"> </td>
<td>OPC Common 1.1 interfaces</td>
</tr>
<tr>
<td><b>OPCDA.pas</b></td>
<td> </td>
<td>OPC Data Access 3.0 (and earlier) interfaces</td>
</tr>
<tr>
<td><b>OPC_AE.pas</b></td>
<td> </td>
<td>OPC Alarms & Events 1.10 custom interfaces</td>
</tr>
<tr>
<td><b>OPCerror.pas</b></td>
<td> </td>
<td>OPC error and status codes</td>
</tr>
<tr>
<td><b>OPCHDA.pas</b></td>
<td> </td>
<td>OPC Historical Data Access 1.1 custom interfaces</td>
</tr>
<tr>
<td><b>OPCSEC.pas</b></td>
<td> </td>
<td>OPC Security 1.0 custom interfaces</td>
</tr>
<tr>
<td><b>OPCtypes.pas</b></td>
<td> </td>
<td>Shared type definitions</td>
</tr>
<tr>
<td><b>readme.htm</b></td>
<td> </td>
<td>This file</td>
</tr>
</table>
<h3>Converting the OPC Definitions</h3>
<p>In each case, the initial conversion of the OPC interfaces was performed
using Delphi's standard 'Import Type Library' function,
specifying the relevant proxy/stub DLL as the type library file. This results
in a set of definitions which works correctly for the most part, but is not
entirely satisfactory. There are several reasons for this:</p>
<ul>
<li>In some cases, certain type name information is missing from the type
library itself. For example, using Microsoft's OLE/COM Object Viewer to
examine the Alarms & Events type library reveals that most of the
struct and enum types have had their original names replaced with names
auto-generated by MIDL. The original type names have therefore been
manually retro-fitted.</li>
<li>There currently appear to be some minor problems with Delphi's
ability to import non-automation type libraries.</li>
<li>In the original C and IDL files, the relevant declarations are
distributed among several different files. For example, the CATIDs for Data
Access 2.0 are defined separately from the other DA 2.0 GUIDs. It is
helpful to combine some of these files to reduce the number of Pascal units
which are required.</li>
<li>There is scope for improving the layout and readability of the files
auto-generated by Delphi.</li>
</ul>
<h3>Acknowledgements</h3>
<p>Some of the work of porting the OPC interfaces to Delphi was performed
initially while working at Eurotherm Limited. Their cooperation in allowing
this code to be published is gratefully acknowledged. The <a href=
"http://www.eurotherm.com/itools/">iTools</a> suite of applications from
Eurotherm includes several OPC client programs developed using Borland
Delphi.</p>
<p>Thanks are also due to the many Delphi OPC developers who have contributed
ideas, suggestions, and corrections.</p>
<h3>Disclaimer</h3>
<p>Although every effort has been made to faithfully convert the original C
and IDL declarations to Delphi, and the results have been used and tested
extensively, I can't of course actually <i>guarantee</i> their
correctness. Neither will I be held responsible for any loss or damage
arising from their use.</p>
<p>I would be grateful to know of any problems with these files.</p>
<p>Mike Dillamore<br />
OPC Programmers' Connection<br />
<a href="http://www.opcconnect.com/">http://www.opcconnect.com/</a><br />
<a href="mailto:opc@opcconnect.com">mailto:opc@opcconnect.com</a></p>
<p>October 5th 2008</p>
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