Fixing Panel IPC477D Communication Loss After WinCC SP5 Upgrade

Problem Summary

After upgrading the WinCC flexible 2008 Runtime on a SIMATIC Panel IPC477D (Windows 7) from Service Pack 3 (SP3) to Service Pack 5 (SP5), the HMI station loses S7 communication to a connected SIMATIC S7-300 CPU 317. The configuration transfer completes without error, ICMP ping between the panel and the CPU succeeds, and the WinCC flexible Runtime emits no system event or diagnostic alarm. Tags and variables that were functional in SP3 stop updating in SP5, and operator screens show static or default values. Reinstalling the Microsoft Visual C++ 2010 x64 Redistributable (already required by WinCC flexible Runtime on x64 systems) has no effect.

The fault is caused by two interacting conditions:

1. The installed WinCC flexible 2008 SP5 lacks the cumulative S7 communication-driver fixes shipped in the later incremental updates for SP5 (Update 1 and Update 2). The base SP5 release contains known communication issues that were resolved in subsequent hotfix bundles.
2. The PG/PC Interface (Set PG/PC Interface) on the Panel IPC477D is no longer bound to the correct access point and physical network adapter after the runtime upgrade. Because the S7 driver reads routing parameters from the PG/PC Interface rather than from the WinCC flexible project, an empty or wrong assignment produces silent failure: the TCP/IP stack is reachable, but the S7 layer cannot find its endpoint.

Both conditions must be remediated to restore communication. The remainder of this document covers affected versions, prerequisites, the recovery procedure, and field verification.

Affected System Configuration

The failure mode has been reproduced on the following combination. Other Panel PC and IPC variants running WinCC flexible 2008 are likely to be affected under the same conditions.

Software Lifecycle Reference

WinCC flexible 2008 is the HMI configuration suite for SIMATIC Panels, Panel PCs, and Multi Panels (except Comfort Panels and TIA-only devices). It was succeeded by WinCC in the TIA Portal, but the WinCC flexible 2008 branch is still maintained for legacy installations. The relevant release levels are:

The SP5 Update 2 entry is published in the Siemens Industry Online Support under entry ID 109757233. Siemens explicitly recommends installing the latest available Update for SP5 on both the engineering station and the runtime station to inherit the S7 communication driver corrections that are not present in the base SP5 image.

Root Cause Analysis

Why Ping Succeeds but S7 Fails

The ICMP ping utility tests the IP layer only. S7 communication uses a session-based protocol on top of TCP (port 102 for S7 Communication, ISO-on-TCP / RFC 1006) and a separate connection handshake that negotiates the S7 communication parameters (rack/slot, PDU size, etc.). When the WinCC flexible Runtime cannot find a valid S7 access point bound to an Ethernet adapter, it does not even attempt to open port 102; the connection failure is silent because the runtime driver never raises a transport-level event. As a result, no entry appears in the WinCC flexible event log, and no alarm is generated on the PLC.

PG/PC Interface in Detail

The PG/PC Interface is a Windows control panel applet installed by SIMATIC software (STEP 7, WinCC flexible, SIMATIC NET) that maps logical S7 access points to physical interfaces:

When WinCC flexible Runtime is uninstalled or upgraded, the installer removes and re-creates the access-point bindings. After the SP3 → SP5 upgrade, the CP_HMI_1 access point is recreated but may default to a different network adapter, or it may be left "unassigned" pending a manual selection. The HMI connection in the WinCC flexible project continues to reference the S7 PLC, but the runtime cannot route the request because its endpoint is unbound.

SP3 to SP5 Driver Change

WinCC flexible 2008 SP3 and SP5 share the S7 communication architecture, but SP5 includes a re-baselined S7 DOS driver stack. Specific symptoms of running with SP5 base (no Update) include:

• No diagnostic event for the affected connection in the WinCC flexible alarm log.
• Tag status "Bad quality" or "No connection" in the HMI tag editor and in runtime.
• Successful reverse-direction test: a maintenance PG on the same network can connect to the CPU and read/write tags through STEP 7, which proves the PLC and cabling are intact.
• No firewall rule added for port 102 (because the connection never opens).

Pre-Upgrade Checklist

Capture the following information before touching the panel. The data is required to roll back if the upgrade is not yet complete and to validate the recovery procedure.

1. Record the WinCC flexible 2008 project version, panel image version, and runtime build number. Open the project in WinCC flexible, then select Project > Properties to read the version; on the panel, open Control Panel > WinCC flexible Runtime > About.
2. Capture the current SP3 runtime version with the installed-software list (Programs and Features in Windows 7).
3. Document the active S7 connection parameters from the project: HMI tag scope, area pointers, connection name, PLC address, rack/slot, and connection type (PROFINET / PROFIBUS / MPI).
4. Capture the network configuration of the Panel IPC477D: IPv4 address, subnet mask, default gateway, and the Windows description of the active Ethernet adapter (Device Manager > Network Adapters).
5. Perform a complete backup of the SP3 runtime image (full disk image or at minimum a system-state backup) and export the WinCC flexible project (.hmi or .fwx file).
6. Verify that the S7-300 CPU 317 firmware supports the desired connection type. CPU 317-2 PN/DP variants (6ES7317-2EK14-0AB0 and later) support PROFINET IO and S7 communication simultaneously. Older CPU 317-2 DP variants (6ES7317-2AK14-0AB0) require PROFIBUS for the second interface.
7. Verify that STEP 7 V5.5 with the matching SP/HF is installed on a maintenance PG for the offline project conversion to SP5, and that the maintenance PG has access to the latest WinCC flexible 2008 SP5 Update from the Siemens support portal.

Step-by-Step Recovery Procedure

Step 1 - Update Engineering and Runtime to the Latest WinCC flexible 2008 SP5 Update

1. On the engineering station, install the most recent WinCC flexible 2008 SP5 Update (Update 2 or later, per Siemens guidance) from entry 109757233 in the Siemens Industry Online Support.
2. Open the existing project, then recompile the project in WinCC flexible 2008 SP5: Project > Compiler > All. Review the "Check" log for unresolved cross-references and unsupported tags.
3. Transfer the recompiled project to the Panel IPC477D using the standard transfer mode (Ethernet / RS-232 / USB / PROFIBUS). Confirm that the runtime restarts and the operator screen loads without a transfer error.
4. On the Panel IPC477D, install the matching WinCC flexible 2008 Runtime SP5 Update (same Update number as the engineering station). The runtime update is a separate installer; do not assume the engineering update alone carries the runtime patches.

Step 2 - Recompile and Transfer the Project

Do not skip the recompile. A project created under SP3 that is opened and saved under SP5 without a full recompile can carry stale connection descriptors. The procedure is:

1. Open the project in WinCC flexible 2008 SP5 (with the latest Update installed).
2. Project > Compiler > Rebuild All (or Compile > All in older builds). Resolve every warning of category "Connection" or "Tag".
3. Transfer the project to the panel using Transfer > Transfer with mode "Serial / Ethernet / USB / PROFIBUS" as appropriate. The transfer must complete without timeout or "Transfer aborted" message.

Step 3 - Configure the PG/PC Interface on the Panel IPC477D

The PG/PC Interface is the silent culprit. It is opened from the Windows Control Panel on the Panel IPC477D; in some IPC477D images the applet is grouped under "Siemens Automation" or "SIMATIC".

1. Open Control Panel > Set PG/PC Interface (in German: "PG/PC-Schnittstelle einstellen").
2. In the "Access Point of the Application" drop-down, select CP_HMI_1 (used for Ethernet-based HMI communication). For PROFIBUS connections, select CP_HMI_2.
3. In the "Interface Parameter Assignment Used" list, select the TCP/IP entry that points to the Panel IPC477D's primary Ethernet adapter (the one physically connected to the S7-300 / PROFINET network). Confirm that the IP address shown matches the network configuration captured in the pre-upgrade checklist.
4. Click OK and close the applet. Windows may prompt to register the access point; allow it.
5. Verify that the assignment persists across reboot. Reboot the panel and re-open the applet to confirm.

Step 4 - Verify S7 Connection Parameters in the WinCC flexible Project

While the project is open on the engineering station, confirm that the S7 connection matches the physical network:

1. Project > Connections > open the affected connection.
2. Verify the "PLC device" matches the CPU 317 variant installed in the cabinet (PROFINET / PROFIBUS / MPI).
3. For PROFINET connections: the "IP address" field must equal the IP address configured in the CPU's PROFINET interface (CPU 317-2 PN/DP only). The "Rack" and "Slot" fields must equal 0 and 2 respectively (S7-300 default PROFINET slot).
4. For PROFIBUS connections: the "MPI/PROFIBUS address" must match the CPU's DP address (default 2), and the baud rate must match the configured DP rate on the network.
5. For area pointers (date/time, PLC job, project ID, etc.), re-confirm the configured DB numbers and offsets. SP5 enforces stricter validation of pointer ranges; out-of-range values cause silent connection failure even if the basic IP parameters are correct.

Step 5 - Restart the WinCC flexible Runtime

1. On the Panel IPC477D, stop the runtime if it is running (Start > Programs > WinCC flexible 2008 Runtime > Close, or use Alt+F4 in the runtime). Wait 5 seconds.
2. Start the runtime from the desktop icon or autostart. Watch the boot-time diagnostic display for S7 connection events.
3. Confirm the connection status with a tag in the project (e.g., a status bit driven by the connection-state area pointer).

PG/PC Interface Reference Configuration

The following settings are required for a single-CPU HMI network with one Ethernet adapter. Adjust for redundant or multi-network topologies.

S7 Connection Parameter Reference

Use the following checklist when verifying or rebuilding the S7 connection in the WinCC flexible project.

Diagnostic Tools and Event Codes

When the runtime is silent, the connection state must be probed with the appropriate tools. The following utilities are part of the standard SIMATIC toolbox and can be run on the Panel IPC477D or on a maintenance PG connected to the same network.

WinCC flexible Runtime Events

WinCC flexible Runtime logs S7 connection events to its internal alarm log. The events most relevant to this issue are:

For a quiet failure (no 14xxxx events), the runtime never even attempted the connection handshake. Re-check the PG/PC Interface binding before debugging the network.

Connection Lifecycle State Machine

STEP 7 Online Diagnostics

On a maintenance PG with STEP 7 V5.5 installed:

1. Open the STEP 7 project containing the CPU 317.
2. PLC > Online > Accessible Nodes. The panel's HMI connection should appear in the list if the PG/PC Interface on the panel is correct AND if WinCC flexible Runtime has opened port 102.
3. PLC > Module Information > Diagnostic Buffer. Look for S7 communication errors and HMI connection-accept/reject entries.

Wireshark / Port Test

If the connection still does not start, run a Wireshark capture on the panel's Ethernet adapter (filter tcp.port == 102) and trigger a tag refresh in the runtime. If no TCP packets are observed, the S7 driver is not attempting to connect - the binding is wrong. If SYN packets are observed but no SYN-ACK is returned, the CPU is the problem (firewall on CPU, IP mismatch, wrong slot).

Verification and Acceptance Test

After applying the recovery procedure, perform the following acceptance checks before returning the panel to production:

1. Operator screen update: open a process screen with at least 5 dynamic values from the CPU 317 (analog readings, counters, status bits). Confirm that values update within the configured acquisition cycle (default 1 s, fast 100 ms, slow 5 s).
2. Alarm test: trigger a process alarm from the CPU side (e.g., set a bit in the configured alarm DB) and confirm the WinCC flexible Runtime displays the alarm within 1 s.
3. PG/PC Interface persistence: reboot the panel twice. After each reboot, confirm that the S7 connection is established automatically and that the PG/PC Interface still shows CP_HMI_1 > TCP/IP > <adapter>.
4. Transfer test: stop the runtime, perform a reverse project transfer from the panel to the engineering station, and confirm the project on the panel matches the engineering source (verify build timestamp in the project properties).
5. Diagnostic buffer check: from the maintenance PG, read the CPU diagnostic buffer and confirm no new "Connection refused" or "Resource exhausted" entries for the panel during the test period.
6. Round-trip tag test: write a value from the HMI (e.g., setpoint via input field), then read the same value back from the CPU in STEP 7 variable table. Confirm the write made it through to the PLC and is read back unchanged.

Troubleshooting Matrix

Frequently Asked Questions