Resolving WinCC Flexible 2008 OP 177B Start Page Soft Key Failure

Problem Summary

On a project built with SIMATIC WinCC flexible 2008 SP1 targeting a OP 177B panel, the function keys (F1–F6) bound to soft-key labels on the configured Start screen produce no event at runtime, while identical soft-key configurations on every other screen in the same project continue to fire their assigned functions correctly. The symptom is reproducible 100 % of the time after a project transfer and is not cured by a panel restart or power cycle. The Start screen itself is otherwise valid: navigation tags update, the screen is drawn, alarms render, and the screen is identified by the runtime as the configured start picture.

This is a configuration-state defect in the WinCC flexible ES, not a panel hardware failure. It is caused by a combination of an unbound soft-key assignment on the Start screen and a stale compilation cache, both of which can be resolved from the engineering station without re-flashing the OP 177B operating system.

Affected Environment

The defect has been observed in the configuration matrix below. Engineering stations and panels outside this matrix are unlikely to exhibit the exact symptom but may share the same underlying root causes.

Reference for runtime behavior and project structure: SIMATIC HMI WinCC flexible 2008 Runtime User Manual.

Root Cause Analysis

WinCC flexible stores soft-key assignments in two scopes: template scope (project-wide, defined on the project template screen) and screen scope (per-screen function list). The Start screen is, internally, the same kind of object as every other screen, but it is the first screen instantiated in the project tree at compile time, which means its compiled soft-key binding is materialised before the global function list is fully resolved.

When the project is built in the following order, two latent defects are introduced:

1. Screens are authored before the soft-key functions are placed on the template. The Start screen therefore captures an "empty" soft-key binding snapshot at first compile.
2. The Engineering Station caches compiled output in a temporary directory under the project root. Subsequent recompiles reuse this cache and never re-link the Start screen against the now-complete global function list.

The visible symptom is that the Start screen's soft keys (F1–F6) have no Press / Release event handler in the generated runtime, although the on-screen labels and graphics render correctly. Other screens, compiled later, bind cleanly because the global function list is fully resolved by then.

Resolution Procedure

Perform the following steps in order. Stop at any step that fails and resolve before continuing.

1. Back up the project

1. In WinCC flexible ES, choose Project > Archive (or copy the entire .hmi project folder including the IM subdirectory).
2. Verify the backup size matches the source project size; a partial backup indicates that the temporary cache directory was not copied and must be excluded from the archive target.

2. Enable "Use global assignment" on every soft key of the Start screen

1. In the project tree, open the Start screen (typically named Start.pdl or Initial Picture).
2. Select each soft key F1 through F6 in turn. Use the Properties window (View > Properties) — not the screen-level properties.
3. Under the General tab of the soft key, locate the property Use global assignment and set it to Yes.
4. Repeat for all six soft keys. The property is per-soft-key, not per-screen; missing even one will leave a dead key.

3. Delete the WinCC flexible temporary files

1. Close the project in WinCC flexible ES.
2. From the WinCC flexible menu, choose Options > Delete temporary files. Confirm the prompt.
3. If the menu option is greyed out (project still open), close the project, then navigate manually to the project directory and delete the IM folder and any *.tmp / *.log files at the project root.
4. Re-open the project from the WinCC flexible Project Manager.

4. Rebuild and transfer

1. Choose Project > Compiler > Generate (or the equivalent in your localised build). This rebuilds the runtime image including the corrected Start-screen soft-key bindings.
2. Choose Project > Transfer > Transfer. In the transfer dialog, confirm target device = OP 177B and the correct interface (MPI address, PROFIBUS, or PROFINET IP).
3. Select Overwrite all on the transfer prompt so the Start screen image is replaced, not appended.

Verification Procedure

After transfer, validate the fix in three layers — first in the PC-based Runtime simulator, then on the panel connected to a test PLC, then on the live PLC.

Layer 1 — WinCC flexible Runtime (PC simulator)

1. With the project open, choose Project > Compiler > Start Runtime. This launches the PC-based RT that mirrors the panel image.
2. Confirm the Start screen loads as the initial picture.
3. Press each of the six soft keys F1–F6. Verify that each one executes its assigned function (tag set, screen change, login dialog, etc.) by watching the configured Output target or by enabling the tag trace.
4. Verify the soft-key labels on the screen match the soft-key function names shown in the project's Softkeys editor under Project > Runtime Settings.

Layer 2 — OP 177B panel on test PLC

1. Connect the OP 177B to a SIMATIC S7-300 / S7-400 test rack on a non-production MPI or PROFIBUS segment.
2. Transfer the rebuilt project to the panel.
3. Cycle panel power to force a clean boot of the Start screen.
4. Press F1–F6 and confirm each event is visible in the STEP 7 VAT or in the WinCC flexible tag simulator.

Layer 3 — Production

1. After Layer 2 passes, transfer to the live OP 177B.
2. Perform an operator walk-through: log in, navigate from Start to process screens, return to Start, and re-test all six soft keys.
3. Capture a project-archive snapshot (Project > Archive) for the change record.

Preventive Configuration Workflow

To prevent recurrence of the Start-screen defect on subsequent projects, follow this authoring order. It guarantees that every screen — Start screen included — captures a fully resolved global soft-key function list at first compile.

1. Create the project and select the OP 177B as the target device before creating any screen.
2. Author the template screen first. Define all six soft-key functions on the template (F1–F6), including Press, Release, and any label or LED feedback.
3. Compile once (Project > Compiler > Generate) to materialise the global function catalogue.
4. Only then create the Start screen and any subsequent screens. Each new screen inherits the now-resolved soft-key bindings.
5. Apply the per-screen overrides on the Start screen with Use global assignment = Yes by default; switch to No only when a screen-local override is intentional and tested.

Firmware, Service Pack, and Compatibility Considerations

The Start-screen defect is independent of the OP 177B image version, but upgrading the WinCC flexible ES removes latent compile bugs that can mask the symptom. Apply the following updates in order:

Confirm the panel image version on the OP 177B at Start Center > Settings > OP Properties > OS Version. If the OS predates WinCC flexible 2008, perform an OS update before transferring the rebuilt project — otherwise the runtime will reject the configuration and the panel will boot to the Start Center with a "Configuration mismatch" message.

Extended Troubleshooting Matrix

Use the table below when the primary resolution does not immediately restore soft-key function on the Start screen. Each row lists a symptom, a likely cause, and a corrective action.

Related Runtime Configuration Considerations

Softkey function list editor

The function list editor is reachable from Project > Runtime Settings > Softkeys. Each of the six soft keys has an expandable function list. Functions placed here are inherited by every screen that has Use global assignment = Yes. Local-screen overrides live in the screen's own function-list editor and take precedence when Use global assignment = No.

Screen property: "Screen is start screen"

Only one screen per project may carry this boolean. The runtime stores the index of this screen in the project binary and uses it at boot to dispatch the first OpenScreen event. If two screens have this flag set (typically a copy/paste artefact), the runtime picks the first one encountered in the project tree and the second becomes unreachable as Start. Audit with Project > Cross-references > Start screen.

Softkey event timing at boot

On a clean boot, the OP 177B RT initializes the area pointers, then loads the Start screen, then fires the screen's Loaded event. Soft-key function lists are bound at screen-load time. If the Start screen's Loaded event handler issues a screen change too quickly (under ~300 ms on OP 177B), the soft-key function list may not yet be bound when the operator presses F1–F6 on the first screen. Insert a Delay of at least 500 ms or move the post-load screen change to a soft-key press instead of Loaded.

Transfer integrity

Always verify the CRC of the transferred runtime against the ES-built image. In WinCC flexible, choose Project > Transfer > Transfer Settings > Verify after transfer. This catches partial transfers that silently leave the Start screen with the old binding even when the project header reports success.

FAQ