Problem Overview
When commissioning a SIMOTION D425 (6AU1425-...) controller, an engineer opens the LAD/FBD editor, presses the Program status icon on the Online toolbar, and sees the network contacts energize in color for less than one second before the network reverts to its static black-and-white representation. The PG/PC link to the CPU is healthy (the SCOUT status bar reports ONLINE), and the CPU property Permit Program Status is enabled, yet the user cannot locate any menu item that changes the operating mode. The symptom is reproducible on every network in every program unit and across multiple LAD/FBD sources.
This behavior is not a bug in the user program, a corrupted download, or a broken fieldbus link. It is the documented runtime behavior of the SIMOTION D4x5 firmware when the device is left in Process mode after download. The fix is to switch the SIMOTION device to Debug (or Test) mode from the Project Navigator before activating program status, and to parameterize the sign-of-life monitoring so the runtime does not drop the link while the engineer watches the live I/O.
Root Cause Analysis
The SIMOTION runtime on the D425 executes user code in one of three selectable operating modes:
- Process mode - production mode selected automatically after a successful download. The runtime emits exactly one status frame on a mode transition and then disables the status channel so that a stuck terminal cannot keep the CPU out of the running production state. The user therefore sees a one-scan flash and nothing more.
- Test mode - the runtime halts at every breakpoint and streams persistent status to the editor.
- Debug mode - the runtime continues executing the user program at full speed while the editor continuously displays program status. This is the recommended mode for observing a live, motion-bearing D425 system without halting the axis controller.
Process mode is the default after every Load to target system action, so any engineer who has never explicitly opened the Operating mode dialog is in Process mode. The Permit Program Status checkbox on the CPU enables the feature, but it does not override the operating mode requirement - the runtime still gates the status stream on the mode bit.
A secondary fault can occur immediately after switching to Debug mode: the PG/PC fails to send a sign-of-life (life-sign) frame inside the configured monitoring time and the CPU exits Debug mode automatically, taking the user back to the one-scan flash. The default 2000 ms monitoring time is too short for any laptop running anti-virus, VPN, or remote-desktop software.
Affected Versions and Components
| Component | Affected versions | Notes |
|---|---|---|
| SIMOTION D425-2 DP | Firmware V4.4 SP3 - V5.5 | All variants including PN and DP/PN combo |
| SIMOTION D435, D445, D455 | Firmware V4.4 SP3 - V5.5 | Same behavior, same fix |
| SIMOTION SCOUT Stand-alone | V5.2 SP1 - V5.4 SP1 | Operating mode dialog under device context menu |
| SCOUT TIA / TIA Portal | V16 - V18 with SCOUT TIA V5.4 SP1+ | Menu relabeled Operating mode & logon |
| LAD/FBD editor | All editor versions | Eye-icon Program status on Online toolbar |
Behavior is independent of the program language (LAD, FBD) and of the unit (axis, TO, cam, programmable IO). The fix described below works on every program unit in the device.
Prerequisites
- Online connection between PG/PC and D425 over PROFINET, PROFIBUS-DP, or Industrial Ethernet. Verify with Target system → Online → Accessible nodes.
- An open SCOUT project that matches the firmware version of the target device. A project that compiles cleanly offline but does not match the firmware will refuse the mode change with diagnostic-buffer entry
F-0148Online version mismatch. - User-rights level Service or higher on the SIMOTION user administration. Operator-level users cannot change the operating mode.
- CPU property Permit Program Status enabled. Without this, the runtime rejects the status command regardless of the operating mode.
- PG/PC interface set to the correct adapter (e.g. S7ONLINE → TCP/IP → Intel I219). The interface selection is at the top of the SCOUT online toolbar.
Step-by-Step Resolution
Step 1 - Confirm Program Status Permission
Right-click the SIMOTION D425 device in the project navigator and select Properties. Open the Settings tab (older builds) or Programming tab (SCOUT TIA). Verify the Permit program status checkbox is set. If it is grayed out, log in as a service user and re-open the dialog. Save and re-load the project to the target if the value was changed.
Step 2 - Select the Device, Not a Sub-Node
Click directly on the SIMOTION D425 node in the project navigator. The operating mode command is only available at the device level. Clicking a sub-node such as Programs, ST sources, or LAD/FBD units opens a different context menu and hides the mode selector.
Step 3 - Open the Operating Mode Dialog
Right-click the device node and choose Operating mode (SCOUT) or Operating mode & logon (SCOUT TIA). A dialog opens with three radio buttons: Process mode, Test mode, Debug mode. The current mode is shown at the top of the dialog.
Step 4 - Select Debug Mode
Choose Debug mode. Use Debug mode (not Test mode) when the D425 is driving a real axis or cam, because Test mode halts the runtime on every breakpoint and can cause axis tracking errors. Debug mode runs the user program continuously and only pauses on explicit single-step actions. If the system is purely a logic test with no motion, Test mode is also valid.
Step 5 - Acknowledge the Safety Prompt
SIMOTION shows a yellow safety-information dialog reminding the engineer that Debug/Test mode disables certain production interlocks. Acknowledge only after confirming that the connected SINAMICS drive is in a safe state: no SBT (Safe Brake Test) active, no active MC_MoveAbsolute command, E-STOP chain closed, and drive enable OFF if the program status session will not issue motion commands.
Step 6 - Parameterize the Sign-of-Life Monitoring
The dialog also shows a Sign-of-life monitoring group. The default value is 2000 ms on the controller side. Increase it to 5000 ms (typical commissioning notebook) or 10000 ms (laptop with anti-virus + remote desktop). The PG/PC side is configured separately in Options → Set PG/PC interface → Diagnostics → Life-sign monitoring and must match the controller value within 200 ms. The two values must always be greater than the worst-case PG scan time, otherwise the CPU drops the link, reverts to Process mode, and the status flash returns.
Step 7 - Confirm with OK
Press OK. The runtime performs an operating-mode transition. The SCOUT online view refreshes and the status indicator next to the device name now shows Operating mode: Debug. The diagnostic buffer records a W-0352 event with the time stamp, the engineer user-name, and the previous mode.
Step 8 - Activate Persistent Program Status
Open the LAD/FBD editor for the desired unit, click the Program status icon (the eye symbol on the Online toolbar) or press Ctrl+F7. The network should now display persistent color-coded status: green for true contacts, blue for false-energized power rails, red for error paths, and yellow for warnings. The variable tooltip shows the live tag value when the cursor hovers over a contact or coil.
Verification
- Network contacts remain color-coded across at least ten OB1 cycles without flickering.
- SCOUT status bar shows Operating mode: Debug.
- The Program status toolbar button stays highlighted (not grayed out) and is not toggled off automatically.
- Hovering a tag shows a live value that updates every scan, not a frozen value.
- The sign-of-life counter in Target system → Diagnostics → Communication increments by one per cycle without a missed-frame event.
Operating Mode Reference
| Mode | Program status | Breakpoints | Runtime effect | Use case |
|---|---|---|---|---|
| Process | One-scan flash only | No | None | Production |
| Test | Persistent, paused at breakpoint | Yes | Halt on breakpoint | Static logic test |
| Debug | Persistent, continuous | Single-step only | None | Live motion test |
Sign-of-Life Monitoring Parameters
| Parameter | Default | Recommended | Notes |
|---|---|---|---|
| Controller monitoring time | 2000 ms | 5000-10000 ms | Must be greater than worst-case PG scan time |
| PG/PC monitoring time | 2000 ms | 5000-10000 ms | Must match controller value within 200 ms |
| Tolerated missed signs (V5.2+) | 1 | 3 | Allows a single slow scan without mode drop |
| Sign-of-life cycle | 500 ms | 1000 ms | Send interval, not the timeout |
State Machine Diagram
Diagnostic Buffer Entries
| Code | Severity | Meaning | Action |
|---|---|---|---|
| W-0352 | Warning | Operating mode changed | Informational; record the change |
| F-0148 | Error | Online version mismatch | Open the matching project offline |
| F-0287 | Error | Sign-of-life timeout, mode reversion | Increase monitoring time on both sides |
| W-0401 | Warning | Permit program status is OFF | Enable in CPU properties and re-load |
Common Pitfalls and Edge Cases
- Permit Program Status is disabled. The runtime rejects the status command in every mode until this property is set. Symptom is identical to Process-mode flash.
- The wrong D4x5 device is selected. Multi-axis projects often have several SIMOTION devices in the tree. Confirm the highlighted node matches the target IP address shown in Accessible nodes.
- SCOUT caches an offline project. Perform Target system → Load → Load to target system and accept the prompt to overwrite the offline project with the online project. Stale offline projects hide the Operating mode command.
- Anti-virus or VPN delays the sign-of-life. Add the SCOUT process to the anti-virus exception list, disable VPN split-tunneling on the commissioning laptop, and set the monitoring time to 10000 ms.
- The PG/PC enters sleep mode. Disable power-saving on the Ethernet adapter; otherwise the link drops and the CPU reverts to Process mode without warning.
- Know-how-protected sources. Protected units display program status only if the password is loaded on the PG. Without it, the eye-icon toolbar is grayed out.
- Non-matching firmware. A V5.3 project targeting a V5.5 device (or vice versa) refuses the mode change with F-0148. Re-target the project to the correct firmware version before going online.
Safety and Production Notes
Related Configuration Locations
| Setting | Path in SCOUT | Path in SCOUT TIA |
|---|---|---|
| Permit Program Status | Device → Properties → Settings | Device → Properties → Programming |
| Operating mode | Device context menu → Operating mode | Device context menu → Operating mode & logon |
| Sign-of-life (controller) | Inside Operating mode dialog | Inside Operating mode dialog |
| Sign-of-life (PG/PC) | Options → Set PG/PC interface → Diagnostics | Options → Set PG/PC interface → Diagnostics |
| User rights | Project → User administration | Project → Security → Users and roles |
Why does ladder program status on the SIMOTION D425 only flash for one scan?
Process mode is the production runtime state and only emits a single status frame on a mode transition, so the editor sees one scan of color before reverting to static. Switch the device to Debug mode from the project navigator context menu to keep status persistent.
What is the difference between Test mode and Debug mode on a SIMOTION D425?
Test mode halts the user program on every breakpoint; Debug mode continues execution at full speed and only pauses during single-step actions. Use Debug mode whenever the D425 is driving a real axis or cam so that motion is not interrupted.
How do I configure the sign-of-life monitoring time on SIMOTION?
Open the Operating mode dialog from the device context menu, set the controller-side monitoring time (5000-10000 ms recommended), and set the same value in SCOUT under Options → Set PG/PC interface → Diagnostics. Both sides must exceed the worst-case PG scan time or the CPU will exit Debug mode automatically.
Do I need to re-download the user program after switching to Debug mode?
No. The operating-mode change only affects the runtime state; the project on the target device is untouched. SCOUT records the change in the diagnostic buffer as warning W-0352 with a time stamp and the user name that made the change.
Can I see program status on a SIMOTION D425 without changing the operating mode?
No. Unlike the S7-1500, the SIMOTION D4x5 family only streams persistent program status in Test or Debug mode. The Permit Program Status checkbox enables the feature but does not override the operating-mode requirement. For a one-shot status snapshot, use a watch table or the variable tooltip in the declaration view.
What should I check if the status still drops back to black after switching to Debug mode?
The runtime is reverting because a sign-of-life frame was missed. Increase both the controller-side and PG/PC-side monitoring time to 10000 ms, add SCOUT to the anti-virus exception list, disable VPN split-tunneling, and verify the Ethernet adapter power-saving option is OFF. The diagnostic buffer will show F-0287 to confirm the sign-of-life timeout.