Resolving CPU 1515SP PC Runtime Communication Failure After Extended Power-Off

The SIMATIC ET 200SP Open Controller CPU 1515SP PC combines a PC-based runtime environment with an S7-1500 Software Controller in a single ET 200SP station. When the controller is powered off for an extended period (typically several days or weeks) and then re-energized, the PLC software controller may fail to establish communication with the Windows-based runtime (WinCC RT Advanced / Professional, or third-party HMI) running on the same device, with no error, diagnostic buffer entry, or LED indication. This article documents the root cause, affected versions, and a step-by-step recovery procedure based on official Siemens product notes and device manuals.

1. Affected Hardware and Software Versions

The behavior is documented for the following Siemens ET 200SP Open Controller variants:

Source: SIMATIC ET 200SP Manual Collection – CPU 1515SP PC Technical Data.

The S7-1500 Software Controller firmware is the relevant component for the loss-of-communication behavior. Versions affected begin with V2.0 through the current production releases. The recovery is described in the Siemens Industry Online Support entry titled "Important updates are available for SIMATIC S7-1500 Software Controllers for all versions beginning with V2.0", which links to the dedicated page "SIMATIC ET 200SP Open Controller (CPU 1515SP PC) – Current Software Controller versions".

2. System Architecture Overview

The CPU 1515SP PC is a hybrid device. It pairs an industrial PC (IPC) running Windows Embedded Standard 7 (WES7) or Windows 10 IoT Enterprise with a software PLC that executes the S7-1500 CPU firmware in a real-time capable container. Communication between the two domains is bridged by the SIMATIC IPC DiagBase and the PC Station interface (a virtual PROFINET / S7 channel).

Key architectural elements:

• IPC side – Windows, WinCC Runtime, optional OPC UA server, SIMATIC IPC DiagBase diagnostics, S7-PCT port 102 binding.
• Software Controller side – S7-1500S firmware executed by the S7-1500 Software Controller, real-time task, scan cycle, OB1 / OB82 / OB121 / OB122 handling.
• Bridge – A protected internal communication channel that carries HMI tags, alarms, and diagnostic events between the WinCC Runtime and the software controller. When this channel is not properly initialized after a long power-off, the PC station remains online but the PLC reports "not reachable" from TIA Portal.

Reference: CPU 1515SP PC Device Manual (PDF).

3. Root Cause Analysis

Siemens documents this behavior in the S7-1500 Software Controller product note. The root cause is a state synchronization mismatch between the S7-1500 Software Controller firmware and the Windows-side PC Station when the device is re-energized after long-term storage. Specifically:

1. The Windows operating system mounts the CFast / SSD volume, the S7-PCT configuration database, and the IPC DiagBase repository.
2. The S7-1500 Software Controller service (SiemensS7SxMgt or equivalent) starts and registers its license / activation blob on the embedded Dongle.
3. When the time gap since last shutdown exceeds a certain threshold (typically > 30 days), the controller's internal internal clock retention buffer and session-state cache can fall out of synchronization with the Windows RTC.
4. The Software Controller starts in RUN, but the OPC / S7 communication endpoint bound to port 102 (ISO-on-TCP / TCP) does not become available on the virtual PC interface until the controller's internal state has been re-initialized through a controlled reconfiguration cycle.

The visible result is the exact symptom reported: no diagnostic buffer entry, no error LED pattern, but TIA Portal and the running HMI cannot establish a logical connection to the S7-1500 software controller. The PROFINET / PROFIBUS slave interfaces typically remain functional because they do not depend on the PC-station communication channel.

4. Pre-Diagnostic Checklist

Before assuming the long-power-off root cause, eliminate the following baseline issues:

If netstat does not show port 102 in LISTENING state, the S7-1500 Software Controller service has either not started, has crashed, or its internal state has not initialized. This is the diagnostic confirmation that you are looking at the long-power-off root cause rather than a TIA Portal project or network error.

5. Step-by-Step Recovery Procedure

Step 1 – Document the current configuration

Before any firmware update, capture the following from the device:

• Article number and serial number (label on the device side).
• Operating system version (Settings → System → About on Windows 10 IoT; winver on WES7).
• Software Controller firmware version (TIA Portal → Online → Accessible nodes → CPU 1515SP PC → Online & Diagnostics → Module information → Firmware).
• Installed SIMATIC software versions (IPC DiagBase, S7-PCT, WinCC Runtime) from the Control Panel.
• Backup of the S7 project (TIA Portal → Project → Archive).

Step 2 – Stop the PC Station and S7-1500 Software Controller service

Open SIMATIC Shell on the device desktop, right-click the PC Station, and select Stop. Then stop the S7-1500 Software Controller service:

or via the Windows Service Manager (services.msc). Wait until both services report Stopped.

Step 3 – Apply the Software Controller firmware update from the Siemens product note

Siemens Industry Online Support publishes the current S7-1500 Software Controller firmware (the V2.x → V3x stream) for the CPU 1515SP PC. Download the file SIMATIC_S7-1500_Software_Controller_V<x.y>.exe and the matching product note. Transfer the file to the CPU 1515SP PC via network share, USB, or remote desktop. Run the installer as administrator.

After the update completes, the installer prompts for a restart. Decline the automatic restart and continue to step 4.

Step 4 – Reset the internal session-state cache

With both services stopped, manually remove the Software Controller's transient state file so the controller rebuilds it on next start:

On the WES7 variant, the path is C:\ProgramData\Siemens\Automation\S7-1500S\Runtime\State. Do not delete the project (.s7p) or license (.lic) files in that directory – only the transient *.cache and *.tmp entries.

Step 5 – Restart in the correct order

Start services in the documented order:

1. Reboot Windows.
2. After login, wait for SIMATIC IPC DiagBase to reach "Ready" (system tray icon turns green).
3. Start the PC Station from SIMATIC Shell.
4. Start the S7-1500 Software Controller service. Verify with netstat -an | findstr :102 that port 102 is now in LISTENING state.

Step 6 – Verify TIA Portal connection

From the engineering station, perform Online → Accessible nodes in TIA Portal V18 or later. The CPU 1515SP PC should appear with its configured IP and PROFINET device name. Double-click the device, open Online & Diagnostics, and confirm the diagnostic buffer now contains a normal RUN / STOP / RESTART sequence without MODULE FAULT or COMM_FAULT entries.

6. Hardening the Project: OB121 and OB122

While the long-power-off root cause is the Software Controller firmware state mismatch, Siemens documentation also recommends loading the programming-error and I/O-access-error organization blocks to prevent the controller from going into STOP if the PC station side loses communication with the software controller during operation.

Insert a new Organization Block (OB) of type Programming error in TIA Portal:

// OB121 - Programming error
IF #OB121_SW_FLT THEN
    // Log error to instance DB
    "dbErrors".PRG_FAULT_COUNT := "dbErrors".PRG_FAULT_COUNT + 1;
    "dbErrors".PRG_FAULT_OB    := #OB121_PRIO;
END_IF;

Insert a new OB of type I/O access error:

// OB122 - I/O access error
IF #OB122_SW_FLT THEN
    "dbErrors".IO_FAULT_COUNT := "dbErrors".IO_FAULT_COUNT + 1;
    "dbErrors".IO_FAULT_BLK   := #OB122_BLK_NUM;
END_IF;

Compile and download the project. The CPU will now remain in RUN even if the PC station bridge loses a single tag update, and the diagnostic counter DB allows post-event analysis.

7. WinCC Runtime Connection Verification

After the firmware update and OB installation, validate the WinCC Runtime end-to-end:

1. Open the WinCC Explorer on the device, select the project, and click Activate.
2. In the RT Advanced runtime, navigate to the connection diagnostics screen (created with the WinCC project template).
3. Confirm the S7-1500 Software Controller channel reports Connected, with cycle time displayed in the 100 – 500 ms range (typical for 100 ms tag acquisition).
4. Force a tag value from TIA Portal (Monitor & Force) and verify it appears in the runtime within one acquisition cycle.
5. Open C:\ProgramData\Siemens\Automation\WinCC RT Advanced\Logs\Connection.log and confirm no 0x80072EE7 or 0x80004005 entries appear after activation.

8. Fault Code and Status Reference

The following table lists the diagnostic states typically observed during the failure and recovery sequence on a CPU 1515SP PC.

9. Alternative Recovery: Cold Restore from Image

If the firmware update and cache reset do not restore port 102, perform a controlled restore from the Siemens recovery image for the CPU 1515SP PC:

1. Back up the active TIA Portal project, the WinCC project, and any custom scripts from C:\Siemens\Automation.
2. Insert the Siemens recovery USB stick and boot the device. The recovery media is the same image used at factory shipment.
3. Select Restore System Partition. The recovery process re-creates Windows, the IPC DiagBase, the S7-1500 Software Controller base image, and the dongle driver.
4. After restore, re-apply the latest S7-1500 Software Controller firmware from the product note, then load the project and the runtime.

The recovery image approach is destructive to any local project state on the controller partition but preserves the dongle-bound license. Allow 45 – 60 minutes for the full restore plus firmware update cycle.

10. Preventive Measures for Long Standstill

For machines that are powered off for more than 30 days between production campaigns, apply the following preventive practices:

• Quarterly power-up: Energize the cabinet for 30 minutes every 90 days so the Software Controller and Windows RTC stay synchronized. This prevents the long-power-off state mismatch from occurring.
• UPS / buffer: Install a SITOP UPS1600 with USB link to the IPC so that controlled shutdown occurs on mains loss, preventing the state mismatch from being triggered.
• Firmware currency: Track the S7-1500 Software Controller product note entries on Siemens Industry Online Support. Apply the latest update during scheduled maintenance windows.
• Project hardening: Always include OB82 (diagnostic interrupt), OB83 (module removal/insertion), OB121 (programming error), and OB122 (I/O access error) in the project. The presence of these OBs keeps the CPU in RUN if any single bridge state temporarily desynchronizes.
• Diagnostic logging: Forward the IPC DiagBase and S7-1500 Software Controller service logs to a central syslog server so the first sign of a desynchronization is visible to operations before the operator notices the HMI loss.

11. Cross-Reference: CPU 1515SP PC2 (TF) Differences

The newer CPU 1515SP PC2 (and the F / TF variants) use Windows 10 IoT Enterprise 64-bit and include 128 GB CFast. The recovery path described above applies unchanged, with the following adjustments:

• Recovery is via the Windows 10 IoT recovery partition, not the WES7E recovery image.
• The S7-1500 Software Controller is delivered as CPU 1505SP (standard) or CPU 1505SP F / CPU 1505SP TF for the fail-safe variants.
• The minimum firmware stream for the F / TF variants is V21.x (current at the time of writing); confirm in the Siemens Industry Online Support entry for the PC2.

Source: CPU 1515SP PC2 (F/T/TF) Device Manual (PDF) and CPU 1515SP PC2 TF + HMI 2kPT Product Finder.

12. Quick Recovery Checklist

Print this checklist for the maintenance panel:

1. Confirm symptom: TIA Portal "not reachable", WinCC Runtime "no connection", port 102 not in LISTENING.
2. Capture article number, firmware, OS version.
3. Stop PC Station and Software Controller service.
4. Apply S7-1500 Software Controller firmware from the Siemens product note.
5. Delete transient *.cache files in C:\ProgramData\Siemens\Automation\S7-1500S\Runtime\State.
6. Reboot Windows, wait for DiagBase green.
7. Start PC Station, then S7-1500 Software Controller service.
8. Verify port 102 in LISTENING, TIA Portal online, WinCC Runtime connected.
9. Confirm OB82 / OB83 / OB121 / OB122 present in project.
10. Log firmware version and date in the maintenance log.