Configuring WinCC OPC DA Server for Cross-Computer Tag Exchange

Problem Context and OPC DA Overview

SCADA stations running SIMATIC WinCC V7.x frequently need to publish their internal or process tags to other computers on the plant LAN — for example, to a historian, a MES terminal, a third-party visualization, or another WinCC client. The legacy method for this is the WinCC OPC DA (Data Access) server, which exposes the entire runtime tag namespace as a COM/DCOM-based OPC item tree. The default programmatic identifier (ProgID) of the server installed on a WinCC operator station is OPCServer.WinCC; once WinCC Runtime is started, every tag declared in the project's Tag Management becomes visible to any compliant OPC client reachable on the network.

This reference documents the end-to-end procedure to enable cross-computer tag exchange with WinCC V7.0 SP3, including the upgrade path from V7.0, the SIMATIC NET prerequisite, the DCOM security hardening required for remote COM instantiation, and the firewall rules needed on Windows 7 64-bit. A parallel note covers modern WinCC Unified RT tag synchronization for projects migrating off classic WinCC.

Prerequisites and Supported Environments

Before the OPC server can be reached from a remote client, verify each prerequisite on both the WinCC server and the OPC client machines.

WinCC V7.0 SP3 ASIA is the regional release referenced in the WinCC V7.0 SP3 release note (Siemens Support entry 55987264); original Windows 7 RTM (without SP1) is not supported by V7.0 SP3 and must be upgraded to SP1 before installing WinCC.

WinCC OPC DA Server Architecture

The WinCC OPC DA server is a Windows in-process COM server (DLL) registered during WinCC setup. It runs only while the WinCC Runtime is active on the station — the OPC item tree is generated from the loaded WinCC project, so stopping Runtime removes the tags from the browse namespace.

The OPC item path the client subscribes to follows the convention:

\\<WinCCServerHost>\OPCServer.WinCC\<TagName>
\\PLC01\OPCServer.WinCC\DB100_DBX0.0
\\PLC01\OPCServer.WinCC\S7_Driver_Connection_01\Motor_Speed

Tags whose source is a WinCC structure tag are exposed as a hierarchical path; numeric and boolean tags are exposed directly. Each tag must be enabled in the WinCC Tag Management — disabled tags are not browsed.

Installing and Verifying OPCServer.WinCC

Run the WinCC V7.0 SP3 setup on the operator station with administrator rights. The OPC option is part of the standard installation but is only activated if SIMATIC NET is also present in some channel configurations.

1. Insert the WinCC V7.0 SP3 / SP3 ASIA DVD or mount the ISO obtained from Siemens Support entry 55987264.
2. Launch Setup.exe as Administrator; choose WinCC Installation and accept the license.
3. In the component tree confirm WinCC OPC Server is selected (default).
4. If SIMATIC NET is required for the channel, install it before WinCC setup completes; the WinCC installer detects SIMATIC NET and registers the matching S7 OPC channels.
5. Reboot when prompted. Log in with the WinCC Runtime user.
6. Open a command prompt and verify COM registration:

   reg query "HKCR\OPCServer.WinCC" /s
   reg query "HKCR\CLSID\{1A2DB3F0-2B5C-11D2-B6F4-0060087A3A0E}" /s

   Both commands must return values without ERROR: The system was unable to find the specified registry key or value.
7. Start WinCC Runtime with the project, then launch any OPC DA browser (e.g. Matrikon OPC Explorer, OPC Quick Client) on the same machine. Connect to OPCServer.WinCC and confirm the project tag list is browsable.

DCOM Security Configuration

Remote OPC clients must instantiate the WinCC COM server over DCOM. Without explicit DCOM permissions the client receives 0x80070005 — Access is denied. Apply the following configuration identically on the WinCC server and the client PCs.

1. Open dcomcnfg from the Start menu.
2. Expand Component Services → Computers → My Computer. Right-click → Properties.
3. Tab Default Properties: enable Enable Distributed COM on this computer; set Default Authentication Level to Connect; set Default Impersonation Level to Identify.
4. Tab COM Security:
   • Access Permissions → Edit Limits: add ANONYMOUS LOGON, EVERYONE, and the OPC client user account; allow Local Access and Remote Access.
   • Launch Permissions → Edit Limits: add Administrators, INTERACTIVE, SYSTEM, and the client user; allow Local Launch and Remote Launch.
   • Launch and Activation Security → Edit Limits: allow Remote Launch and Remote Activation for the same principals.
5. Switch to DCOM Config, locate OPCServer.WinCC, right-click → Properties:
   • Tab General: set Authentication Level to Default or Packet Privacy if on an untrusted segment.
   • Tab Location: tick Run application on the following computer → enter the WinCC server hostname.
   • Tab Security: override with Use custom launch permissions and Use custom access permissions; add the same principals as in step 4.
   • Tab Identity: select The launching user if the client user has matching credentials, or This user and enter a domain account that exists on the WinCC server with read/write access to the project directory.
6. Repeat steps 1–4 on every OPC client PC.

SIMATIC NET Installation Considerations

If the WinCC project reads process values via SIMATIC S7 / PROFIBUS / PROFINET channels, SIMATIC NET must be installed and configured on the operator station. SIMATIC NET ships its own OPC server (OPC.SimaticNET) which can coexist with the WinCC OPC server.

After installing SIMATIC NET, restart the WinCC Configuration Studio and re-open the Tag Management. Channels that previously failed to populate (status 0x02 = BadCommunicationError) will now show valid handle sets, and the OPC browse tree will include the SIMATIC NET addresses.

Firewall and Network Configuration

Windows Firewall blocks DCOM by default. Configure explicit rules or open the required ports.

1. Open wf.msc → Inbound Rules → New Rule.
2. Allow the program %ProgramFiles%\Siemens\Automation\WinCC\bin\CCOpcServer.exe for Domain, Private, and Public profiles.
3. Create a port rule allowing TCP 135 (DCOM endpoint mapper).
4. Open the dynamic RPC port range. Microsoft default is TCP 49152–65535 for Windows 7; restrict it via registry:

   reg add HKLM\SOFTWARE\Microsoft\Rpc\Internet /v Ports /t REG_MULTI_SZ /d 5000-5010 /f
   reg add HKLM\SOFTWARE\Microsoft\Rpc\Internet /v PortsInternetAvailable /t REG_SZ /d Y /f
   reg add HKLM\SOFTWARE\Microsoft\Rpc\Internet /v UseInternetPorts /t REG_SZ /d Y /f
   net stop "Windows Firewall" & net start "Windows Firewall"

5. Allow inbound ICMPv4 Echo Request for diagnostics only; remove after commissioning.
6. Disable SMB signing only on the OPC pair if required by legacy clients — not recommended for production.

From the client, validate end-to-end connectivity:

Test-NetConnection -ComputerName <WinCCServer> -Port 135
Get-Service -ComputerName <WinCCServer> -Name "WinCC Runtime" | Select Status, Name

Configuring OPC Clients for Tag Exchange

On the client PC, install any OPC DA 2.05a / 3.0 compliant client. Common choices: OPC Quick Client (bundled with Matrikon), KEPware, Inductive Automation Ignition OPC-DA, Siemens OPC Scout (V10 / V13).

1. Add a new OPC DA server connection. Enter the remote node as \<WinCCServerHost>\OPCServer.WinCC (double-backslash syntax required by COM).
2. Authenticate using the configured DCOM identity user.
3. Browse the namespace. The hierarchy shows the WinCC server name → connection → tag.
4. Add a group with desired update rate (typical 250–1000 ms). For high-speed data logging use 100 ms and disable dead-band filtering by setting the group PercentDeadband to 0.
5. Subscribe to the items. Verify a quality code of 0xC0 (Good) on the items; 0x04 = BadConfigurationError means the tag is not declared; 0x08 = BadCommunicationsError means the underlying channel is offline.

For programmatic access (C#, Python with OpenOPC, Node.js with node-opc-da), instantiate the server with the correct CLSID and item path. Example with Python + OpenOPC:

import OpenOPC
opc = OpenOPC.client()
opc.connect('OPCServer.WinCC', host='WinCCServer01')
print(opc.list(tags=True, recursive=True))
print(opc.read(['DB100_DBX0.0', 'Motor_Speed']))
opc.close()

Tag Synchronization in WinCC Unified RT

Projects migrating to WinCC Unified V17+ replace classic OPC DA with OPC UA and provide built-in tag synchronization between HMI tags and connected PLC tags. The synchronization behavior is configured per tag collection via the runtime settings panel described in the Settings for tags (RT Unified) documentation.

For pure cross-PC tag exchange in Unified, publish the HMI tags via OPC UA server on port 4840 (default) and consume them from another Unified station or third-party OPC UA client using opc.tcp://<UnifiedPC>:4840.

Verification and Diagnostics

After completing installation and DCOM configuration, validate the OPC DA server is reachable from the client.

1. From the client, open the OPC client tool and select Connect to Server. The tool must list OPCServer.WinCC on the WinCC server hostname.
2. Add a group, browse, and add three tag types: a boolean, a 16-bit integer, and a 32-bit float. Confirm quality = Good (0xC0) and a non-zero timestamp.
3. Force a value change in WinCC (e.g. via the Graphics Designer test mode). Verify the change appears on the client within one update cycle.
4. Disconnect and reconnect. The OPC server should re-instantiate without restarting WinCC Runtime.
5. Check the WinCC station logs: %ProgramFiles%\Siemens\Automation\WinCC\diagnose\ → WinCC_Sys_<date>.log. Look for OPC-related entries; OPCServer.WinCC started confirms registration.
6. Use the Windows event viewer: Applications and Services Log → OpcEnum for COM activation traces.

If quality flags remain at 0x01 (BadConfigurationError) after restart, the tag has been removed from Tag Management but is still subscribed by the client — refresh the group and re-add the items.

Troubleshooting Matrix

Migration Notes: V7.0 to V7.0 SP3 and Beyond

The most common cause of "cannot find OPC server" in legacy installations is running WinCC V7.0 RTM on Windows 7 64-bit without SP1. Microsoft ended mainstream support for Windows 7 RTM on April 9, 2013, and WinCC V7.0 SP3 is the last SP that explicitly supports that OS family.

1. Verify current WinCC version in Help → About WinCC Explorer.
2. Download the latest V7.0 SP3 / SP3 ASIA or V7.4 / V7.5 media from Siemens Support entry 55987264 or via the Siemens Industry Online Support portal under Product Support → WinCC V7.
3. Schedule a maintenance window — the upgrade restarts the WinCC service.
4. Back up the project directory (\<server>\WinCCProjects\<project>\) and the WinCC archive directories.
5. Run the installer, choose Update, and select the existing project for migration.
6. Recompile the OS, then start Runtime. Validate OPC browsing from the client.
7. Long-term, plan migration to WinCC Professional / WinCC Unified on TIA Portal to use OPC UA and eliminate the COM/DCOM attack surface.

FAQ