Restoring PROFIBUS DP Fault Messages in PCS 7 V8.0 - Module Driver Wizard Regeneration and Diagnostic OB Configuration

Following an upgrade to SIMATIC PCS 7 V8.0 SP2, missing PROFIBUS DP failure messages are restored by regenerating the automation station module drivers and synchronizing diagnostic organization blocks. In PCS 7 V8.0, peripheral faults rely on system block OB_DIAG1 executing in OB82, OB83, OB86, and OB122. If hardware was imported using the Standard catalog profile or compiled with 'Changes Only', the Driver Generator does not link the updated diagnostic structure. To resolve, open HW Config to verify the PCS 7 catalog profile, execute a full CFC compilation with 'Generate module drivers' enabled, and perform a full OS compilation with 'Tags and Messages' checked.

Executive Summary

Upgrading industrial control systems from legacy PCS 7 versions (such as V7.0 or V7.1) to PCS 7 V8.0 SP2 introduces substantial modernizations to the Advanced Process Library (APL) diagnostic framework. However, commissioning engineers frequently report that field bus dropouts, ET 200M interface module disconnections, and PROFIBUS cable severance events no longer generate alarms in the WinCC Alarm Logging runtime banner. While the CPU diagnostic buffer logs the hardware interrupt, the operator station receives no corresponding system message. This failure occurs when the CFC Driver Generator is bypassed during engineering compilation or when legacy diagnostic blocks remain unmigrated. This guide details the internal diagnostic mechanics of PCS 7 V8.0 and provides the definitive recovery procedure.

CFC Module Driver Wizard Mechanics in PCS 7 V8.0

The CFC Driver Generator (Module Driver Wizard) is an automated system compiler that scans the hardware station configuration (HW Config) and generates dedicated diagnostic driver charts:

For every PROFIBUS DP master system, it creates SUBNET (FB106) blocks.
For every modular remote I/O station (e.g. ET 200M / ET 200S), it creates RACK (FB107) blocks.
For every signal module, it creates MOD_D1 / MOD_HA blocks and links their diagnostic outputs (Mode, DataXchg) to technological channel drivers (Pcs7DiIn, Pcs7AnIn).

If an engineer upgrades the software but compiles the AS with 'Changes Only', the compiler skips regenerating the underlying driver infrastructure, leaving broken pointers to obsolete library blocks.

Diagnostic Organization Blocks and Event Processing

The S7-400 CPU evaluates peripheral field bus faults through dedicated asynchronous Organization Blocks (OBs):

OB82 (Diagnostic Interrupt): Triggered when an intelligent I/O module detects internal faults, wire break, or power loss.
OB83 (Insert / Remove Module Interrupt): Triggered when modules are removed or inserted under voltage.
OB86 (Rack Failure Interrupt): Triggered when an entire PROFIBUS DP slave station disconnects or loses bus communication.
OB122 (I/O Access Error): Triggered when the CPU attempts cyclic I/O read/write to a missing peripheral address.

In PCS 7 V8.0, the system block OB_DIAG1 is placed in each of these OBs to capture the event record, format the associated text values, and invoke ALARM_8P to transmit the alarm directly to WinCC OS.

Diagnostic Driver Architecture: OB_DIAG1 vs Classic Drivers

In classic PCS 7 versions, diagnostic messages were distributed across multiple individual driver blocks. In PCS 7 V8.0, Siemens consolidated diagnostic event handling into OB_DIAG1 (FB118). When an OB86 event occurs, OB_DIAG1 extracts the logical base address and station number from the local variable temporary stack (OB86_MDL_ADDR), identifies the affected slave in the plant hierarchy, and emits an alarm with exact station metadata.

Hardware Diagnostic Configuration Matrix

The following table compares the diagnostic behavior, block assignments, and compilation requirements for bus faults:

Hardware EventTriggering OBAssigned System BlockGenerated WinCC MessagePrerequisite Engineering SettingPROFIBUS Cable SeveredOB86OB_DIAG1 & RACK'DP Slave Failure: Station 'HW Config: Diagnostic addresses assignedET 200M Module PulledOB83 / OB82OB_DIAG1 & MOD_D1'Module Pulled / Diagnostic Fault'Active bus modules installedSensor Wire BreakOB82MOD_D1 -> Pcs7AnIn'Wire Break / Bad Quality'HF module with channel diagnostics enabledDP Master System FailureOB86SUBNET'PROFIBUS Master System Interrupted'CP 443-5 / CPU internal DP port mappedI/O Access TrapOB122OB_DIAG1'I/O Access Error: Address 'Driver Generator inserted into OB122

Step-by-Step Restoration Procedure

Method 1: Verifying HW Config Catalog Profile and Diagnostic Addresses

Open HW Config for the target AS in SIMATIC Manager.
Ensure all remote I/O interface modules (IM 153-2, IM 151-1 HF) are placed from the PCS 7 Profile.
Double-click each slave interface module, select the Operating Parameters tab, and confirm that Diagnostic Interrupt is enabled.
Note the assigned Diagnostic Address (e.g. 16#03FE / 1022).
Save and compile HW Config.

Method 2: Full CFC Compilation with Driver Regeneration

Open any CFC chart in the AS program.
Select Chart > Compile > Charts as Program from the menu.
Select the radio button Entire program.
Check the box Generate module drivers.
Click OK and monitor the compilation log. Verify that OB_DIAG1 is inserted into OB82, OB83, OB86, and OB122.
Download the program to the CPU (note: a CPU stop may be required if runtime groups were restructured).

Method 3: Full OS Compilation and Message Synchronization

In SIMATIC Manager, right-click the OS project and select Compile.
In the OS Compilation Wizard, select Entire OS and check Tags and messages.
Complete the OS compilation, activate WinCC Runtime, and test bus fault annunciation.

Verification

To verify that PROFIBUS DP failure messages are annunciated correctly:

Controlled Hardware Fault Test: On an active remote I/O station (e.g., IM 153-2), power down the interface module or unplug the PROFIBUS connector.
WinCC Alarm Banner Verification: Confirm that within 1 second, an unacknowledged alarm appears in the top WinCC Alarm Banner stating 'Rack Failure: DP Master System X, Station Y'.
Alarm Clearance Test: Reconnect the bus connector. Confirm that the alarm updates to 'Gone' state and clears upon operator acknowledgment.

Limitations and Operational Precautions

Production Downtime Risk: Generating module drivers across an entire multiproject can modify organizational runtime groups. Never execute full AS compilation and download on an operating production facility without planned downtime.
Custom Third-Party DP Devices: Non-Siemens DP slaves utilizing generic GSD files do not generate automated diagnostic messages unless mapped to specialized driver blocks (MOD_PAL).
Diagnostic Buffer Overflow: If repeated bus flutters occur, disable problematic nodes in HW Config or activate flutter suppression in the channel drivers to avoid overflowing the CPU Diagnostic Buffer.

Engineer FAQ

Can I compile module drivers for only one remote I/O rack?

No. The CFC Driver Generator evaluates the entire hardware configuration and all CFC charts globally; it cannot be executed for isolated racks.

Why does WinCC show 'Driver disconnected' instead of a rack failure alarm?

If the OS is compiled without 'Tags and Messages', WinCC loses the symbolic message definitions, displaying generic driver connection errors rather than technological alarm texts.

What happens if OB86 is not downloaded to the S7-400 CPU?

If a PROFIBUS rack failure occurs and OB86 is not present in the controller load memory, the CPU transitions immediately to STOP mode by operating system design.

Technical References

Related Tags

https://industrialautomation.net/search?query=simatic-pcs7
https://industrialautomation.net/search?query=profibus-dp
https://industrialautomation.net/search?query=driver-wizard
https://industrialautomation.net/search?query=fault-diagnostics

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Restoring PROFIBUS DP Fault Messages in PCS 7 V8.0 - Module Driver Wizard Regeneration and Diagnostic OB Configuration