Configuring PLC Tags in WinCC Faceplates in TIA Portal

Overview

Faceplates in SIMATIC WinCC (TIA Portal) are reusable HMI screen objects built once and instantiated across multiple screens or process units. A faceplate is a self-contained visualization that exposes a fixed tag interface — the contract between the faceplate and the calling screen. To animate or evaluate faceplate internals (e.g., a button's Click event, a value display, or a visibility expression) you bind events to interface tags, not directly to PLC tags. PLC tags are then assigned to those interface tags per instance.

This indirection is the root of the most common faceplate question: why can I only see HMI tags in the events dialog, and not the PLC tags I want to control? The answer is the two-stage binding model:

1. Inside the faceplate type, you create interface tags (also called properties or faceplate tags). These are declared in the editor under Interface > Properties_Faceplate (V13/V14) or Configuration > Interface (V15+ and RT Unified).
2. At the faceplate instance on a screen, each interface tag is bound to an HMI tag or a PLC tag. The PLC tag flows into the faceplate only at this point.

Prerequisites

Faceplate Tag Architecture

Every faceplate type maintains three scopes of tags. Mixing them is the source of most binding errors.

Per the Siemens Faceplates Instruction Manual (V14, PDF), the Tags tab contains tags available only inside the faceplate and connected directly to contained objects. They cannot be bound to PLC tags from the outside. The Interface section is the only place where the faceplate exposes a binding surface to the calling screen.

Creating Interface Tags (Properties_Faceplate)

1. In the project tree, right-click Faceplates under your HMI device and choose Add new faceplate. Name it (e.g., FP_Valve).
2. Open the faceplate type for editing (double-click).
3. In the project tree under the faceplate, expand Interface > Properties_Faceplate. The default name varies by version: Properties_Faceplate in V13/V14, Faceplate_Properties from V15.1, or the configurable interface in V16+ Unified.
4. Add a new property. Configure:

Repeat for each property the faceplate needs: StartCommand, StopCommand, Running, Fault, TagPrefix, etc. The number of properties is limited by the runtime; V14 supports up to 500, V17+ Unified supports 1000+.

Wiring Interface Tags to Faceplate Objects and Events

Once properties are declared, they appear in the Properties pane of every object inside the faceplate, alongside HMI tags, internal tags, and constants.

1. Open the faceplate body and draw four buttons. Name them btnStart, btnStop, btnAck, btnReset.
2. Select btnStart. In Properties > Events > Click, choose Set bit as the function list entry.
3. In the function list dialog, the tag picker shows three tabs: Constants, HMI tags, Faceplate tags. Expand Faceplate tags > Properties_Faceplate and select StartCommand.
4. The function list now contains SetBit "Properties_Faceplate".StartCommand (V13/V14 syntax). In V16+ Unified the syntax uses the configured interface name: SetBit "Faceplate_Properties".StartCommand.
5. Repeat for the other three buttons: StopCommand, AckCommand, ResetCommand.

Save the faceplate. At this point the faceplate has no knowledge of any PLC. It simply toggles its own interface properties.

Binding PLC Tags at the Faceplate Instance

1. Open the screen where the faceplate will be used (e.g., Screen_Overview).
2. Drag the faceplate from the library/task card onto the screen. The instance appears with a default name (e.g., FP_Valve_1).
3. Select the instance. In Properties > Interface > Properties_Faceplate, every declared property is listed with an empty value field.
4. For StartCommand, click the value field. The tag picker shows HMI tags. Browse to the PLC tag (e.g., HMI_TagTable.Motor1_Start) or to a raw PLC tag if the connection is direct.
5. For an HMI tag that already points at %DB5.DBX0.0 (a S7-1500 BOOL data block bit), simply select that HMI tag — the runtime reads the bit from the PLC.

For V16+ Unified, the dialog is renamed Properties > Faceplate_Properties and the binding is configured under Configuration. See the Siemens TIA Portal V20 Faceplate Interface Documentation for the exact dialog tree.

Tag Type Mapping Between PLC and Faceplate

The data type of the property must be compatible with the data type of the bound PLC/HMI tag. Mismatches compile but raise warnings at runtime, or the value is silently truncated.

Dynamic Tag Names (Multiplexing)

For pop-up faceplates that must work on any of 200 motors, use a tag prefix or multiplexing (V15+):

1. Declare a property TagPrefix of type WString[32].
2. Declare StartCommand as Bool.
3. In the Interface editor (V15.1+), set StartCommand to Multiplex. Bind its source expression to TagPrefix + ".Start".
4. At the instance, set TagPrefix = "DB_Motor[1]". The runtime resolves the tag at compile time or first display.

Version-Specific Notes

If you are stuck on V13, you cannot use multiplexing. Instead, build one faceplate per instance, or use a script with the HMIRuntime.Tags object to resolve the tag at runtime.

Script-Based Binding (Advanced)

For dynamic PLC tag binding that is not known at compile time, use VB or C script inside the faceplate:

' VBScript example: read a tag whose name is built at runtime
Dim tagName, value
tagName = SmartTags("TagPrefix") & ".Running"
value = HMIRuntime.Tags(tagName).Read
SmartTags("Properties_Faceplate").Item("Running").Value = value

In RT Unified (V16+), the equivalent is JavaScript using the HMIRuntime object:

let prefix = Tags("TagPrefix").Read();
let value = Tags(prefix + ".Running").Read();
Tags("Faceplate_Properties").Item("Running").Write(value);

Verification Procedure

1. Compile the HMI project (Compile > Software (rebuild all)). Address warnings about unresolved tags before continuing.
2. Download to the HMI runtime (RT Professional, RT Advanced, or panel).
3. Open the screen with the faceplate. Force the PLC tag from the PLC online view (TIA Monitor & Force). Confirm the faceplate property updates.
4. Click the faceplate button. Confirm the corresponding PLC tag flips in the PLC online view. If it does not:

• Check the connection status in the HMI diagnostics screen.
• Verify the PLC tag is accessible (read/write, not write-protected by access level).
• Confirm the security setting in the user administration is not blocking the write.

5. From the HMI, force the PLC tag to TRUE. Confirm the indicator in the faceplate (e.g., running lamp) turns green.
6. Stop the runtime. Recompile. Confirm no warnings appear in the output window.

Troubleshooting Matrix

Performance and Best Practices

• Keep the number of properties per faceplate below 30. More than that inflates compile time and the runtime memory footprint.
• Prefer Bool over Int for individual bits — the runtime cycles BOOL tags faster.
• Reuse faceplate instances: instead of creating 100 separate faceplates, build one and multiplex the tag prefix.
• Do not place scripts inside frequently triggered events (e.g., Value change on a 100 ms tag). Use On-demand triggers.
• Compile the HMI project to a separate folder before each download. This lets you roll back if a binding change breaks runtime behavior.
• Use the Cross-reference tool (Ctrl+Shift+F3) to verify every faceplate instance has all its properties bound. Unbound defaults are a common runtime surprise.

Frequently Asked Questions