Resolving TIA V15 WinCC 7.4 PLCSIM V15 Communication Errors

Problem Overview

Engineers integrating TIA Portal V15 with WinCC V7.4 Runtime over PLCSIM V15 frequently encounter a communication fault where the S7-1200/S7-1500 channel does not establish. In WinCC Explorer under Tag Management > S7-1200, S7-1500 Channel > OMS+ > [connection], the connection status indicator fails to display a green tick (healthy state) and instead shows two orange vertical tick marks. The same TIA Portal project goes online without error, confirming that PLCSIM V15 itself is reachable, but the WinCC V7.4 RT channel cannot bind to the simulator through the configured access point.

The root cause is a mismatch between the Access Point of the Application assigned in the WinCC connection parameters and the PG/PC Interface assignment in the Windows Control Panel. Because the WinCC 7.4 RT and PLCSIM V15 run in different logical interface spaces on the same PC, the channel DLL must be explicitly pointed at the PLCSIM virtual adapter before the S7-1500/1200 connection can complete its TCP open.

Affected Software Stack

Siemens release notes for WinCC V7.4 SP1 Update 1 explicitly state that communication with PLCSIM V15 for S7-1200 and S7-1500 is supported only after applying this update. Without it, the OMS+ channel returns intermittent connection aborts because the SIMATIC NET layer below it has not been synchronized with the PLCSIM V15 transport.

Root Cause Analysis

The fault chain is rooted in how WinCC V7.4 resolves its S7-1200/S7-1500 channel DLL to a network interface. The relevant configuration points are:

1. WinCC connection parameter — Access Point of the Application. In WinCC Explorer, navigate to Tag Management > S7-1200, S7-1500 Channel > OMS+ > [your connection] > right-click > Connection Parameters. Each connection holds a logical access point name, for example S7ONLINE, PLCSIM, or a user-defined name. This is the name the channel DLL passes to the SIMATIC NET layer.
2. Windows Control Panel — PG/PC Interface (Set PG/PC Interface). This is where the named access point is bound to a physical or virtual network adapter. The access point name in step 1 must map here to PLCSIM (the virtual Ethernet adapter installed by PLCSIM V15) or to S7ONLINE depending on the routing path.
3. SIMATIC NET installation. The SIMATIC NET PC Software provides the Access Point of the Application dialog and registers the PLCSIM and S7ONLINE interface modules. If SIMATIC NET is missing or older than V14 SP1, the PLCSIM access point will not appear in the list, and any WinCC connection that targets it will fail with the orange tick state.

When the access point in the WinCC connection differs from the binding in the PG/PC Interface — for example, the channel points at S7ONLINE but the PG/PC interface binds S7ONLINE to a real Intel NIC — the OMS+ channel sends the S7 connect request to the physical adapter instead of the PLCSIM loopback, and PLCSIM V15 never receives the open. The connection status stays at fault, displayed as two orange vertical tick marks.

Prerequisites

• Local administrator rights on the engineering PC (required to install SIMATIC NET and modify the PG/PC interface).
• TIA Portal V15 or V15.1 installed with PLCSIM V15 component enabled.
• WinCC V7.4 SP1 Update 1 (or later) installed and licensed.
• SIMATIC NET PC Software V14 SP1 (or V15 SP1) installed.
• A compiled S7-1200 or S7-1500 program downloaded into PLCSIM V15 with the same instance name the WinCC project will reference.
• WinCC V7.4 project with the S7-1200/S7-1500 channel added via Tag Management > Add New Driver > SIMATIC S7-1200, S7-1500 Channel.

Step-by-Step Solution

Step 1 — Apply the WinCC 7.4 SP1 Update 1

1. Close WinCC Explorer and stop the WinCC Runtime.
2. Run the WinCC V7.4 SP1 Update 1 installer with administrative elevation.
3. Reboot the workstation when prompted.
4. Verify the installed build in Control Panel > Programs and Features > SIMATIC WinCC > Version. The build must be at minimum 7.4.1.1.

Step 2 — Confirm the SIMATIC NET Access Point Catalog

1. Open Start > SIMATIC > SIMATIC NET > Communication Settings > Set PG/PC Interface.
2. From the Access Point of the Application dropdown, confirm that PLCSIM and S7ONLINE are present. If PLCSIM is missing, reinstall SIMATIC NET PC Software V14 SP1 (or later) and re-register the PLCSIM interface module.
3. Set Interface Parameter Assignment Used to PLCSIM (TCP/IP) > PLCSIM Virtual Ethernet Adapter for the row whose Access Point of the Application equals PLCSIM.
4. Set the same row for S7ONLINE only if TIA Portal and WinCC must share the same interface; otherwise leave S7ONLINE bound to a physical NIC.

Step 3 — Bind the WinCC Channel to the PLCSIM Access Point

1. Open the WinCC V7.4 project in WinCC Explorer.
2. Browse to Tag Management > S7-1200, S7-1500 Channel > OMS+ > [your connection].
3. Right-click the connection and select Connection Parameters.
4. In the dialog, set:
   • IP Address: the loopback address of the PLCSIM V15 instance (typically 127.0.0.1 or the project-bound virtual IP).
   • Access Point: PLCSIM (must match the PG/PC binding from Step 2).
   • CPU Type: S7-1500 (or S7-1200 if you are simulating a 1200).
   • Connection Type: TCP/IP.
5. Press OK to commit the change.

Step 4 — Synchronize the PG/PC Interface

1. Reopen Set PG/PC Interface.
2. Select PLCSIM from the Access Point of the Application dropdown.
3. Confirm that the assigned interface is the PLCSIM Virtual Ethernet Adapter (the one created by PLCSIM V15 during installation).
4. Click OK to save.

Step 5 — Restart the Runtime Stack

1. Close WinCC Explorer.
2. Stop the CCWrite, CCAlg, and CCProjectMgr Windows services (or simply reboot the PC, which is more reliable in V7.4 SP1 Update 1).
3. Start PLCSIM V15, download the S7-1500 program, and place the CPU in RUN.
4. Launch WinCC Runtime.
5. Return to WinCC Explorer and observe the connection status indicator. It must show a single green tick; the orange ticks are cleared.

Verification

Use the following checks to confirm the channel is healthy after the fix:

1. WinCC Explorer status indicator. The connection under OMS+ must show a green tick. Two orange ticks indicate a fault; one orange tick indicates a degraded state (degraded only happens when the channel reports partial data, which is not applicable to PLCSIM).
2. WinCC Channel Diagnosis tool. Open Start > SIMATIC > WinCC > Tools > Channel Diagnosis. The connection must report CONNECTED and the partner IP must match the PLCSIM virtual adapter.
3. Tag test. Create a temporary internal tag bound to a known DB bit (for example, DB1.DBX0.0 in the PLCSIM V15 project). Force the bit in PLCSIM and confirm the tag value updates in WinCC within 2 seconds.
4. Event log sanity. In the Windows event viewer under Applications and Services Logs > Siemens Automation > WinCC, no entries with Event ID 0x0000C1A0 (channel abort) or 0x0000C1A4 (interface not bound) should appear.
5. Network loopback test. From an elevated command prompt run ping <PLCSIM virtual IP>. It must respond from 127.0.0.1 within 1 ms. If it routes elsewhere, the PG/PC binding is wrong.

Channel Status Indicator Reference

Access Point Reference Table

Troubleshooting Matrix

Why S7-1500 Fails More Often Than S7-1200

The S7-1500 channel DLL uses a different transport handshake (optimized PUT/GET with PDU size negotiation) than the S7-1200 channel. PLCSIM V15 implements the S7-1500 handshake on the loopback adapter, but the handshake completes only when the access point is bound to the PLCSIM virtual adapter. If the access point is bound to a real NIC, the S7-1500 PDU open reaches the physical interface and never returns because no S7-1500 device exists on that subnet. The S7-1200 channel uses a simpler transport that occasionally succeeds through the default Windows routing table when the S7-1200 image in PLCSIM answers on the loopback anyway. This is why engineers see S7-1200 green, S7-1500 orange on the same workstation.

Common Configuration Pitfalls

• Mixing TIA V15 with SIMATIC NET V13. SIMATIC NET V13 does not register the PLCSIM V15 access point. The WinCC connection parameter will not list PLCSIM, and any attempt to type it manually produces an invalid handle.
• Running PLCSIM V15 and WinCC V7.4 RT as different Windows users. The PG/PC interface is per-user. The user that launches WinCC RT must own the PLCSIM binding. Switch to a single service account for both processes in production test rigs.
• Multiple PLCSIM instances. Only one PLCSIM V15 instance can occupy the virtual adapter at a time. If a second instance is started, the first instance's TCP listener drops and the WinCC connection aborts. Close extra PLCSIM sessions before launching WinCC RT.
• Hyper-V virtual switch binding. If the engineering PC runs Hyper-V with an external virtual switch on the same NIC used by PLCSIM, the virtual switch can intercept loopback traffic. Disable the virtual switch or set its adapter metric higher than the PLCSIM adapter.
• Windows Fast Startup. On Windows 10, Fast Startup hibernates the kernel network stack between boots. The PLCSIM virtual adapter sometimes reports a stale state. Disable Fast Startup when commissioning PLCSIM-based test rigs.

Advanced Diagnostic: Reading the WinCC Channel Log

1. Open WinCC Explorer > Tools > Channel Diagnosis and enable verbose logging to C:\ProgramData\Siemens\Automation\WinCC\ChannelDiag.log.
2. Reproduce the fault by stopping and starting the WinCC RT.
3. Inspect the log for these event markers:
   • AccessPointNotFound — the WinCC connection requested an access point not registered in SIMATIC NET. Fix by reinstalling SIMATIC NET.
   • ConnectTimeout 0x0000274C — TCP connect to the partner IP timed out. Fix by verifying the PLCSIM virtual IP and the PG/PC binding.
   • PDUNegotiationFailed — S7-1500 PDU size could not be agreed. Fix by matching the PLCSIM instance configuration to the WinCC connection (CPU type field).
4. After applying a fix, delete the log file and re-test to confirm the marker is cleared.

Intermittent TCP Connection Drops

After applying the fix above, some workstations still report intermittent drops every few hours. This is usually caused by Windows TCP keepalive defaults interacting poorly with the PLCSIM loopback. Apply the following registry tuning to stabilize the channel:

Windows Registry Editor Version 5.00

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters]
"KeepAliveTime"=dword:0000003C
"KeepAliveInterval"=dword:00000001
"TcpMaxDataRetransmissions"=dword:00000005

Set KeepAliveTime to 60 seconds and KeepAliveInterval to 1 second. This forces the loopback to detect a dead PLCSIM session within one minute, allowing WinCC to reconnect automatically without flooding the channel log.

Migrating to TIA V15.1 or V16

If the workstation can be upgraded, the same procedure applies but with cleaner default bindings:

• TIA V15.1 with WinCC 7.5 SP1 Update 1 — PLCSIM V15.1 access point is auto-registered and the PG/PC interface dialog includes a one-click Bind to PLCSIM button.
• TIA V16 with WinCC 7.5 SP2 — the S7-1500 channel default CPU type is auto-detected from the PLCSIM instance, eliminating the S7-1200-vs-S7-1500 mismatch.
• TIA V17 with WinCC Runtime Professional — the PLCSIM and WinCC RT run in the same process boundary, removing the access-point layer entirely. This is the recommended path for new test rigs.

When upgrading, uninstall the previous TIA version cleanly, remove the old PLCSIM virtual adapter via Device Manager > Network Adapters > Uninstall, and reboot before installing the new TIA version. Stale virtual adapters from older PLCSIM builds have been observed to keep a binding even after a new TIA version is installed.

Field-Proven Commissioning Checklist

1. Verify WinCC V7.4 build is at least 7.4.1.1 (SP1 Update 1).
2. Verify SIMATIC NET PC Software build is at least V14 SP1.
3. Verify the PLCSIM access point exists in the PG/PC Interface dialog.
4. Set the WinCC connection parameter Access Point to PLCSIM.
5. Set the PG/PC Interface binding for PLCSIM to the PLCSIM Virtual Ethernet Adapter.
6. Close TIA Portal online view to release the PLCSIM session.
7. Start PLCSIM V15, download the program, set CPU to RUN.
8. Start WinCC Runtime.
9. Confirm green tick in WinCC Explorer.
10. Force a known bit in PLCSIM and confirm WinCC tag updates within 2 seconds.
11. Save the project and export the channel configuration as a backup.

FAQ