Resolving WinCC 7.4 STEP 7 V5.6 Set PG/PC Interface Conflict

1. Problem Overview

Engineers running a side-by-side installation of SIMATIC WinCC V7.4 and SIMATIC STEP 7 V5.6 on the same engineering station frequently observe one or more of the following symptoms when WinCC Runtime is activated or when the Set PG/PC Interface dialog is opened from either application:

• The Set PG/PC Interface dialog is empty or only shows the S7ONLINE entry without any usable access points such as TCP/IP→S7ONLINE, PC internal→S7ONLINE, or Named pipe→S7ONLINE.
• S7DOS service fails to register, returning Error 1068 ("The dependency service or group failed to start") or Error 7000 ("The service was not started").
• PLCSIM disconnects immediately after WinCC Runtime is started. The S7-PLCSIM virtual adapter disappears from the Access Point of the Application dropdown.
• WinCC reports WinCC cannot connect to the AS, channel diagnosis shows HmiESpS7.dll returning 0x80040514 / WCCOA·S7·0003 ("Connection to partner not established").
• STEP 7 Manager refuses to Go Online with SF message "Online: No online connection found to target station" while WinCC Runtime is active.

The combination of WinCC V7.4 + STEP 7 V5.6 SP1/HF1 is the most common trigger because the WinCC V7.4 base installer ships an older S7DOS (S7DOS Helper Service) and an older S7OTBXSX.DLL (STEP 7 Online Toolbox) than the versions required by STEP 7 V5.6. When WinCC is installed after STEP 7 V5.6, it downgrades shared online components; when installed before STEP 7 V5.6, the WinCC installer does not refresh the components at all.

2. Root Cause Analysis

Three independent mechanisms cause the symptoms above. Identify which one applies before applying a fix.

2.1 Shared component version rollback

WinCC V7.4 (released 2016) was qualified against STEP 7 V5.5 SPx. WinCC V7.4 SP1 extends support up to STEP 7 V5.5 + SP4. STEP 7 V5.6 introduced updated versions of:

When both products are installed, only the most-recently-installed winstall-driven package "wins." Older PC-Internal (Softnet) and PLCSIM virtual adapters registered by the other product are removed from %ProgramFiles%\Siemens\Automation\pgpc\pgpc.ini and from the registry under HKLM\SOFTWARE\Siemens\SINEC\Protocols.

2.2 SIMATIC Compatibility Tool mismatch

The official SIMATIC Compatibility Tool defines the legal product combination matrix. As of the V5.6 release, the legal WinCC ↔ STEP 7 pairings for engineering stations are:

WinCC V7.4 + STEP 7 V5.6 is not listed as a supported engineering-station pair in the compatool; it is treated as a downgrade and the WinCC installer scrubs V5.6 components back to V5.5 vintage.

2.3 PG/PC Interface auto-assignment

The Set PG/PC Interface dialog binds the application layer S7ONLINE to a transport. WinCC and STEP 7 share that binding through the registry key:

HKLM\SOFTWARE\Siemens\SINEC\S7ONLINE\Params\AccessPoint\S7ONLINE\Default

A corrupted or missing value here displays an empty dropdown. The most frequent trigger is a half-completed installation where S7DOS and S7SVC services failed to start on first boot.

3. Pre-Flight Diagnostic Procedure

Run the following checks before changing anything. Save outputs for Siemens support if escalation is required.

1. Capture installed SIMATIC packages:
   D:\> "C:\Siemens\Automation\simatic_net_sws\setup\collect.bat" > %TEMP%\sni_collect.txt (or via SINEC NCM — Diagnostics on older stations).
2. Verify service status:

   sc query S7DOS
   sc query S7OPCX
   sc query s7svc

   Each service should be in STATE : 4 RUNNING.
3. Verify registered COM objects:

   regsvr32 /u C:\Program Files\Siemens\Automation\S7WSVXEX\s7oexp.dll
   regsvr32    C:\Program Files\Siemens\Automation\S7WSVXEX\s7oexp.dll

   Both commands must return "DllUnregisterServer / DllRegisterServer succeeded."
4. Inspect the PG/PC binding file:

   type "%ProgramFiles(x86)%\Siemens\Automation\pgpc\pgpc.ini"

   Look for [S7ONLINE] section with Default=TCP/IP→S7ONLINE (or PC internal→S7ONLINE when using PLCSIM).
5. Run the SIMATIC Installation Check tool:
   "C:\Program Files\Siemens\Automation\Setup\CheckTool\AsdCheckInst.exe" /report
6. Generate the WinCC diagnostic trace:
   In WinCC Explorer enable Diagnostics → Performance → Tag Logging / Connection Diagnostics, reproduce the failure, then export via CCDiagnosticFiles.exe.

4. Solution A — Align Versions via the Compatibility Tool

This is the recommended path. It restores the legal pairing Siemens documents.

1. Open the SIMATIC Compatibility Tool, choose Engineering → HMI → WinCC V7.x, then verify the target STEP 7 version.
2. If a legal WinCC V7.4 pair exists for STEP 7 V5.6 within your hotfix baseline (e.g. WinCC V7.4 SP2 Update 14 + STEP 7 V5.6 SP1 with HF01), note the build numbers and proceed to step 3. Otherwise pick the legal alternative WinCC V7.5 SPx and switch projects using the WinCC project migrator.
3. Run Start → SIMATIC → Product Notifications and capture the current build. Compare to the compatool's recommended bundle.
4. Apply the required hotfixes using the Siemens Industry Online Support entry IDs (WinCC V7.4 SP1 → 109754693, STEP 7 V5.6 SP1 → 109751320) in the correct order: STEP 7 hotfixes before WinCC hotfixes.
5. Reboot. Reopen Set PG/PC Interface; the dropdown should now list all access points.

5. Solution B — Repair the Set PG/PC Interface Database

If the version pair is fixed but the dialog remains empty, rebuild the pgpc layer.

1. Close all SIMATIC applications.
2. Open an elevated command prompt and stop the services:

   net stop S7DOS
   net stop s7svc
   net stop s7OPCX

3. Back up and replace the interface database files:

   ren "%ProgramFiles%\Siemens\Automation\pgpc\pgpc.ini" pgpc.ini.bak
   ren "%ProgramFiles%\Siemens\Automation\pgpc\pgpc.cfg" pgpc.cfg.bak

4. Re-register the access-point APIs in this exact order:

   cd /d "%ProgramFiles%\Siemens\Automation\pgpc"
   regsvr32 s7pgintf.dll
   regsvr32 pcasbase.dll
   regsvr32 s7otbxdx.dll

5. Restart the services, then launch the Set PG/PC Interface dialog. Choose S7ONLINE → TCP/IP → S7ONLINE (TCP/IP→S7ONLINE) for S7-300/400, or PC internal→S7ONLINE for PLCSIM operation.

6. Solution C — Repair the STEP 7 Installation

Use this when STEP 7 V5.6 was installed before WinCC and the WinCC installer rolled S7DOS back to V7.4 vintage.

1. Insert the STEP 7 V5.6 DVD or mount the corresponding SIMATIC field. Run setup.exe with elevation.
2. Select Repair / Update, confirm the target path C:\Program Files\Siemens\Automation, and tick the S7DOS Helper Service, STEP 7 Online Toolbox, and SIMATIC Diagnosis Monitor packages.
3. Allow the installation to overwrite WinCC-bundled components. Do not uncheck any boxes for "shared" packages.
4. Reboot. Verify the WinCC project still loads — WinCC V7.4 SPx accepts the newer S7DOS, but in Compatibility Mode for the S7-300/400 channel.

7. Solution D — Restore WinCC Runtime ↔ PLCSIM Connectivity

When WinCC disconnects from PLCSIM specifically (a common symptom of WinCC V7.4 + PLCSIM V5.6 mismatch), execute the following.

1. Stop the WinCC Runtime in WinCC Explorer → Computer → Properties → Startup.
2. In PLCSIM, set PLC → Mode → Run with Trigger and confirm the IP/port pair matches the WinCC channel (192.168.0.1 / 102 by default).
3. In Set PG/PC Interface, select PLCSIM→S7ONLINE (added by PLCSIM install) or TCP/IP→S7ONLINE loopback pointing to 127.0.0.1.
4. Confirm WinCC channel parameter S7·TCP·IP / Address of AS equals the PLCSIM target IP.
5. Restart WinCC Runtime; check Status of the connection — it should turn green within 5 s. If it remains red, capture C:\ProgramData\Siemens\Automation\Logfiles\S7.log for analysis.

8. Inline State Machine (Installation Order)

To prevent the conflict entirely, follow this configuration state machine when provisioning a fresh engineering station:

9. Preventive Maintenance & Field Caveats

• Always validate via the kompatool before adding a new SIMATIC product to a station with WinCC running. The compatool is updated after every hotfix release.
• Avoid TIA Portal mixed installs on classic WinCC stations. TIA Portal V16+ installs s7dos112.dll, which cannot register alongside the older S7DOS.exe WinCC uses. Either segregate into separate boot partitions or run TIA and WinCC in Hyper-V / VMware VMs.
• Anti-virus impact. Several real-time AV scanners block the S7DOS service on cold start, returning the Error 7000 symptom. Add %ProgramFiles%\Siemens\Automation to the AV exclusion list.
• Windows Server Core. WinCC V7.4 is not supported on Server Core editions; the missing GUI shell prevents S7DOS from being re-registered by the PG/PC tray app.
• User Account Control. Without elevated rights, the Set PG/PC Interface dialog silently writes settings to %LOCALAPPDATA% instead of HKLM, creating a per-user binding that disappears after logout.
• License keys. Repairing STEP 7 does not invalidate WinCC licenses, but uninstalling and reinstalling STEP 7 V5.6 will request license re-transfer from the Automation License Manager.

10. Verification Checklist

1. Open Start → SIMATIC → Set PG/PC Interface. Confirm at least TCP/IP→S7ONLINE and PC internal (local)→S7ONLINE appear in the Interface Parameterization Used list.
2. Open STEP 7 Manager. Options → Set PG/PC Interface → Application Interface; the dropdown must be non-empty and match the entry selected in step 1.
3. Start PLCSIM, load the project, click Run. Open WinCC Runtime; the status bar should show green connection within 5 s and no further yellow/red transitions.
4. Force a tag read from WinCC: open Graphics Designer → WinCC Online TrendControl — trend values must update within the configured refresh cycle (default 1 s).
5. Run the WinCC Channel Diagnostics (Start → SIMATIC → WinCC → Channel Diagnostics) and confirm 0 connection errors over a 5-minute window.
6. Reboot; repeat steps 1 and 5. Persistent state across reboots confirms the fix is durable.

11. Quick Reference Matrix

12. Escalation Path

If, after executing Solutions A and C in sequence on a fresh-rebooted station, the Set PG/PC Interface dialog still drops all S7 entries:

1. Generate a SIMATIC Support Request package via Start → SIMATIC → Product Notifications → Create Request.
2. Attach the CCDiagnosticFiles.exe output, the pgpc.ini backup, and the exported Windows event logs for sources S7DOS, S7OPCX, and Automation License Manager.
3. Submit through the Siemens Industry Online Support portal using the WinCC product tree (entry ID 109754693 as the reference).