Enabling Function Keys on Siemens KTP400 Basic PN in TIA Portal

Overview: Why Function Keys Appear Disabled on a KTP400 Basic PN

The SIMATIC KTP400 Basic PN (catalog number 6AV2 123-2DB03-0AX0) is a 4-inch widescreen HMI panel that combines a touch interface with four physical function keys (F1–F4). The panel is configured in TIA Portal using WinCC Basic (or higher, in compatibility mode) and communicates with the controller (e.g., S7-1200, S7-1500, LOGO!) over PROFINET.

A common commissioning complaint is that the F-keys look "dead": clicking on a function key in the screen editor produces no configurable events, the Properties > Events list is empty, or the Configure button is greyed out. The root cause is almost never a hardware failure; it is the global function-key assignment option that is enabled by default on every screen and template of a Basic Panel project. When global assignment is active, the F-keys are reserved for project-wide navigation actions (e.g., change screen, log on, log off) defined once at the panel level, and the per-screen event interface is suppressed.

This article documents the exact procedure to release F1–F4 for local screen-level or template-level event programming on a KTP400 Basic PN, the architectural differences between Basic and Comfort panels, and the verification steps to confirm the keys are firing in runtime.

Prerequisites

1. Hardware: SIMATIC KTP400 Basic PN (6AV2 123-2DB03-0AX0) with firmware V14.0.0.0 or later. Earlier firmware (V12/V13) uses an identical procedure but renders dialogs in older style.
2. Software: TIA Portal V14 SP1 or higher with WinCC Basic/Comfort installed. The KTP400 Basic PN is supported by all WinCC Basic versions; runtime simulation can be performed with the integrated RT Basic.
3. Project structure: A compiled TIA Portal project containing the HMI device, at least one PLC connection (PROFINET or MPI/Profibus depending on order number), and at least one screen with the function keys visible in the screen layout.
4. Tags and PLC connection: At least one configured HMI tag pointing to a PLC address — required to demonstrate press/release actions during verification.
5. Siemens Knowledge Base access for the primary reference: Entry ID 109747178 - "How do you configure the function keys of SIMATIC Basic Panels?"

Function Key Architecture on Basic Panels

Basic Panels (KTP400 Basic, KTP700 Basic, KTP900 Basic, KTP1200 Basic) and 2nd-generation Basic Panels (KTP400 Basic 2nd, KTP700 Basic 2nd) share a simplified runtime compared to Comfort Panels. The runtime distinguishes three assignment scopes:

Differences Between KTP400 Basic PN and KTP400 Comfort

Many field engineers assume the two KTP400 variants behave identically because they share a form factor. The runtime, however, is significantly different:

The Comfort panel's runtime can hold both a global and a local action for the same key and will execute the local action in the active screen. The Basic panel runtime executes the global action and ignores the local event. This is why a programmer who has migrated a project from Comfort to Basic frequently sees the local events become "dead" — the F-key still fires, but the local handler is bypassed.

Step-by-Step: Enable Per-Screen Function Key Events

Follow this procedure in TIA Portal to release the F1–F4 keys for local programming on a KTP400 Basic PN.

Step 1 — Open the HMI Device Properties

1. In the project tree, expand the HMI station (e.g., HMI_1 [KTP400 Basic PN]).
2. Double-click Properties in the lower pane, or right-click the device and select Properties.
3. Navigate to General → Function keys.
4. Note the current state of the four keys. By default each key is mapped to a built-in global function such as Change screen (F1, F2) or Logon / Logoff (F3, F4).

Step 2 — Disable "Use Global Assignment" for a Specific Screen

1. In the project tree, expand Screens and double-click the screen (e.g., Screen_1) you want to control locally.
2. Select the screen background (click an empty area, not a control).
3. In the Inspector window open the Properties tab, then the General section.
4. Find the entry Assignment → Use global assignment. The default is checked.
5. Uncheck Use global assignment.

Step 3 — Wire F-Key Events in the Screen

1. With the screen still open, click the F-key button in the screen layout (e.g., the labelled rectangle at the bottom of the screen representing F1).
2. The Inspector window now shows Properties → Events for that key.
3. Click the Press event, then click the small ... button on the right to open the event list.
4. Choose an action — for example, SetBit → select an HMI tag that is connected to a PLC bit (e.g., "HMI_to_PLC".StartMotor).
5. Repeat for the Release event (e.g., ResetBit on the same tag) if the application requires a falling-edge action.
6. Repeat Steps 3.1–3.5 for F2, F3, F4 as required.

Step 4 — Configure Template-Level F-Key Events (Optional)

If multiple screens should share the same F-key behavior, place the events in the template instead of duplicating them in every screen:

1. Project tree → HMI → Templates → double-click the active template.
2. Open the Properties of the F-key representation in the template.
3. Configure the Press / Release events exactly as in Step 3.
4. Screens using the template will inherit the behavior automatically.

Step 5 — Compile and Download

1. Right-click the HMI device → Compile → Software (rebuild all).
2. Resolve any warnings; the common warning "Function key F1 is assigned globally" disappears after Step 2.
3. Transfer the project to the panel: right-click HMI device → Download to device → Software (all).

Verification: Confirm the F-Keys Fire in Runtime

Compile-time success is not enough — the F-key wiring must be proven at runtime. Use the following checks in order:

Check 1 — Visual Confirmation in WinCC RT Basic

1. Start the runtime simulation: right-click HMI → Start runtime → select RT Basic.
2. Navigate to the screen where you disabled global assignment.
3. Press F1 (on the PC keyboard F1 acts as the panel's F1).
4. The configured action — for example, a screen change, a tag toggle, or a value entry — must occur.

Check 2 — Online Tag Trace

1. Open an HMI tag table (project tree → HMI Tags).
2. Right-click the tag used in the F-key event and select Monitor/Modify.
3. Press F1 on the runtime; the tag value must toggle exactly when the key is pressed.

Check 3 — PLC-Side Cross-Check

1. Open the PLC tag table in the S7-1200/1500 project.
2. Monitor the bit the HMI tag points to.
3. Press F1 on the panel; the PLC bit must transition to TRUE within one PROFINET cycle (typically 1–4 ms).

Check 4 — Operator Panel LED (Comfort only — skip for Basic)

If the project is later migrated to a Comfort panel, the same procedure also exposes the F-key LED tag in the area pointer. On the Basic PN, this step is N/A.

Common Pitfalls and Field-Worked Solutions

Comparing Configuration Paths: Global vs. Template vs. Local

For a typical KTP400 Basic PN application with 4 keys, the following decision tree is recommended:

1. All screens need the same behavior (e.g., F1 = "Go to start", F2 = "Acknowledge alarms") → configure once at the HMI device level. The runtime overhead is the lowest.
2. Most screens need a common behavior, but a few need local overrides → keep the global assignment for the common keys, disable global assignment only on the screens with overrides, and use the template for the common behavior.
3. Every screen has unique F-key actions → disable global assignment on every screen and wire the F-keys locally. Note: this maximizes runtime look-up time but provides maximum flexibility.

Function Key Area Pointer: Using the PLC Bit Set

Even with the global assignment disabled, the Function key area pointer remains active. This is a 4-word (8-byte) area in the PLC that the panel writes to whenever a function key is pressed, regardless of which scope is active. The layout is:

Configure the pointer at: HMI device → Properties → Connections → Area pointer → Function key. Point it to a data block in the S7-1200/1500, e.g., DB100.DBW0 (offset 0). The PLC sees the same bit pattern whether the F-key is wired to a global, template, or local action — the area pointer is independent of the assignment scope.

Migration Notes: KTP400 Basic PN to KTP400 Comfort

When a Basic PN project is migrated to a Comfort panel (or upgraded to a KTP1200 Basic 2nd with the Comfort firmware option), the function-key handling changes:

1. The Comfort runtime supports simultaneous global and local F-key events. A local Press event fires even when a global action is also defined for the same key.
2. Basic panel projects use a 4-bit area pointer. Comfort projects expand this to a 32-bit pointer when enabled in the area pointer settings.
3. F-key LEDs are exposed on Comfort panels as additional bits in the function-key area pointer — useful for indicating key acknowledgement back to the operator.
4. Procurement: Comfort panels cost 3–5× the Basic PN equivalent. The migration decision should be driven by required features (PROFINET IRT, archives, scripts, Sm@rtServer) rather than F-key flexibility alone.

Firmware and Software Compatibility

For panel firmware update procedure and recovery if the download fails, refer to the Siemens Knowledge Base entry 109747178 and the KTP400 Basic PN operating instructions (entry 109751546).

Field Commissioning Checklist

1. Verify the panel part number on the nameplate matches 6AV2 123-2DB03-0AX0 (or compatible variant).
2. Confirm PROFINET link: panel port 1 (X1) connected to the CPU's PROFINET port, link LED green.
3. In the TIA Portal project, check Devices & Networks → the HMI is assigned to the PLC subnet.
4. Compile → rebuild all → no warnings remaining.
5. Download to device → select PG/PC interface → HMI → Ethernet.
6. After panel reboot, open the configured start screen and press each F-key.
7. Confirm in the PLC tag monitor that the expected bit transitions occur.
8. Document the final F-key map in the project functional specification for future maintenance.

FAQ