S7-PLCSIM TCP/IP Driver Communication Recovery in WinCC OS Simulation Following Service Pack Updates

In SIMATIC PCS 7, when WinCC OS Simulation loses communication with S7-PLCSIM over the TCP/IP channel following an update from PCS 7 V9.0 SP1 to V9.0 SP2 UC3, the failure is caused by S7DOS driver registration corruption or obsolete channel settings in the WinCC S7 Protocol Suite. Service pack updates refresh low-level S7DOS communication drivers, frequently breaking the virtual connection to PLCSIM.TCPIP.1. To restore communication, open WinCC Tag Management, navigate to 'SIMATIC S7 PROTOCOL SUITE -> TCP/IP -> System Parameters', verify that the Logical Device Name is set to 'PLCSIM.TCPIP.1', reset the PG/PC interface to 'PLCSIM.TCPIP.1', and re-download HW Config and NetPro to PLCSIM.

Executive Summary

Following system maintenance or service pack deployments (such as upgrading an Engineering Station from PCS 7 V9.0 SP1 to V9.0 SP2 UC3), software engineers routinely discover that previously operational S7-PLCSIM simulation environments fail. While the S7-400 CPU simulation starts and CFC charts download without error, starting OS Simulation in WinCC results in complete communication breakdown: all dynamic tags show disconnected status (0x01 / #), and the WinCC Channel Diagnosis tool reports 'Disconnected' under the TCP/IP channel. This guide details the S7DOS communication pipeline between WinCC and PLCSIM, explains driver registry changes in SP2 UC3, and provides the complete recovery sequence.

Architecture and Fundamental Mechanics

The communication architecture connecting WinCC OS Simulation to S7-PLCSIM coordinates multiple software layers:
1. S7DOS Virtual Loopback Subsystem:
Classical S7-PLCSIM (V5.4 SP8) relies on the SIMATIC Device Drivers (S7DOS) layer to emulate hardware network controllers. When TCP/IP simulation is selected, S7-PLCSIM registers the virtual device PLCSIM.TCPIP.1 with the Windows network stack.
2. WinCC SIMATIC S7 Protocol Suite Channel:
WinCC communicates with controllers using the SIMATIC S7 Protocol Suite channel DLL (s7communic.dll). Under the TCP/IP sub-channel, the driver queries the Windows registry for the device assigned to S7ONLINE. During physical plant operation, S7ONLINE points to a physical network card (e.g., CP1623.ISO.1 or Intel(R) Ethernet). During simulation, S7ONLINE must point to PLCSIM.TCPIP.1.
3. Root Causes of Failure Post-Upgrade (SP1 to SP2 UC3):
- S7DOS Driver Overwrite: Upgrading to SP2 UC3 replaces core communication DLLs (s7oiehsx.dll), resetting virtual device registrations in the registry to physical adapters.
- NetPro Gateway Desynchronization: If NetPro connections were compiled under SP1, the compiled S7 connection IDs may not align with the updated S7-PLCSIM memory image until a fresh 'Compile everything' is executed in NetPro.
- WinCC Service Mode Lockout: If the project was migrated into Service Mode, Session 0 isolation blocks the TCP/IP loopback to the desktop PLCSIM instance.

Step-by-Step Implementation Procedure

Reset and Reconfigure PG/PC Interface:
a. Close SIMATIC Manager, S7-PLCSIM, and WinCC Explorer.
b. Open Windows Control Panel -> 'Set PG/PC Interface (32-bit)'.
c. Select Access Point: 'S7ONLINE (STEP 7)'.
d. In the interface parameter list, select 'PLCSIM.TCPIP.1'.
e. Click OK to confirm.
Verify Logical Device Name in WinCC Tag Management:
a. Open the OS project in WinCC Explorer.
b. Open 'Tag Management'.
c. Expand SIMATIC S7 PROTOCOL SUITE.
d. Right-click on 'TCP/IP' and select 'System Parameters'.
e. Select the 'Unit' tab: locate the field 'Logical device name'.
f. Ensure the logical device name is set to 'PLCSIM.TCPIP.1' (or matches the S7ONLINE setting).
g. Check connection properties under TCP/IP: confirm IP address matches the AS CPU's configured IP in HW Config.
Execute Full Hardware and Network Recompilation:
a. In SIMATIC Manager, open HW Config -> Station -> Save and Compile.
b. Open NetPro -> Network -> Save and Compile (Select 'Compile everything').
c. This regenerates the exact S7 connection tables matching the updated SP2 compiler.
Sequence the PLCSIM Startup and Download:
a. Launch S7-PLCSIM from SIMATIC Manager.
b. In the PLCSIM window, select 'TCP/IP' mode.
c. In HW Config, download hardware to PLCSIM.
d. In NetPro, download connections and gateways to PLCSIM.
e. In SIMATIC Manager, download the S7 program to PLCSIM.
f. Switch the simulated CPU to 'RUN-P'.
Launch OS Simulation and Monitor Channel Health:
a. In SIMATIC Manager, select the OS object -> Options -> OS -> Start OS Simulation.
b. Open the WinCC Channel Diagnosis tool (Start -> Siemens Automation -> Channel Diagnosis).
c. Expand SIMATIC S7 PROTOCOL SUITE -> TCP/IP.
d. Confirm that the connection status displays a green icon with status 'OK'.

Verification

In WinCC Channel Diagnosis, verify that the connection counter shows active telegram exchanges (incrementing Read/Write requests).
Open a graphic picture in OS Simulation: confirm that all dynamic tags display live values without yellow triangles or # symbols.
Force a digital input in S7-PLCSIM: confirm that the corresponding block icon in WinCC changes color within 500 ms.

Limitations and Operational Precautions

S7-PLCSIM V5.4 TCP/IP simulation does not support routing across external network subnets; all simulated nodes (AS and OS) must reside locally on the same engineering station operating system.

Engineer FAQ

Why did the S7-PLCSIM connection fail after updating to PCS 7 V9.0 SP2?

The service pack update refreshed the S7DOS communication drivers and reset the S7ONLINE access point, severing the virtual loopback connection between WinCC and PLCSIM.