WinCC Action Scripts: Switching Pictures via Tag Trigger

1. Overview

Siemens WinCC runtime supports automatic screen (picture) navigation driven by process values. When a tag changes state—e.g., a mode selector bit, a recipe phase, or a fault flag—the HMI should switch to the matching process picture without operator intervention. The mechanism for this in WinCC V7.x, WinCC Professional (TIA Portal), and the legacy WinCC flexible runtime is the Global Action (or Scheduled Task) executed by the C-Editor scripting engine.

This reference covers three production-proven methods:

• SSMChangeWorkField – for Split Screen Manager (base picture switching in WinCC V7.x).
• OpenPicture – the standard picture-change call for permanent area, work area, or modal dialogs.
• Picture Window attribute write – for TIA Portal WinCC and embedded Picture Window objects whose PictureName property can be driven by a tag or by C action.

All three approaches share the same first step: configure a trigger on the C action. The trigger tells the WinCC scripting runtime when to evaluate the script. Without a properly configured trigger the script will not fire and the picture will not change.

2. Prerequisites

For the full WinCC V7.x scripting API see the SIMATIC HMI WinCC V7.5 Scripting (C) manual. For TIA Portal see the SIMATIC WinCC Professional V17 Programming and Operating Manual.

3. Method 1 – Global Action with OpenPicture (C-Editor)

The OpenPicture function is the workhorse for picture changes. It opens a picture in a target work area defined by the runtime configuration.

3.1 Create the global action

1. Open WinCC Explorer.
2. Right-click Global Scripts → C-Editor and select New Action (or open an existing one).
3. Name the action descriptively, e.g. ac_ModePictureSwitch.
4. Paste the C function call into the editor.

3.2 C source for a binary mode tag

// ac_ModePictureSwitch.c
// Triggered cyclically or on @ModeSelector change
// @ModeSelector = 0 → Picture_Manual.pdl
// @ModeSelector = 1 → Picture_Automatic.pdl

if (GetTagBit("ModeSelector") == 0)
{
    OpenPicture("Picture_Manual.pdl");
}
else
{
    OpenPicture("Picture_Automatic.pdl");
}

3.3 Function reference

4. Method 2 – Split Screen Manager (SSM)

The Split Screen Manager (SSM) is a WinCC V7.x component that allows a base picture to be subdivided into up to four fields (top, bottom, left, right). To swap one of those fields from C, call SSMChangeWorkField.

4.1 SSM configuration

1. Open Computer → Properties → Split Screen Manager in WinCC Explorer.
2. Define the layout: e.g., 1 row, 1 column → single work field.
3. Assign the field index (typically '1' for the primary work field).
4. Activate the SSM checkbox in the startup list of the WinCC runtime.

4.2 C source for SSM

// Field index '1' = primary work field (top-left in a 2x2 layout)
if (GetTagBit("ModeSelector") == 0)
{
    SSMChangeWorkField('1', "Picture_Manual.pdl", TRUE);
}
else
{
    SSMChangeWorkField('1', "Picture_Automatic.pdl", TRUE);
}

4.3 SSMChangeWorkField parameter matrix

5. Method 3 – Picture Window (TIA Portal WinCC)

In WinCC Professional / Comfort Panels the Picture Window object is the modern equivalent of an SSM field. Its PictureName property accepts both a static string and a dynamic tag-driven expression. Either drive it from a tag or set it from a C action via SetProperty / SetTag.

5.1 Drive PictureName from a tag (no script)

1. Create a string tag PictureTarget of type WSTRING[80].
2. PLC writes the picture name (e.g., "Screen_Manual") into that tag.
3. In the HMI screen, select the Picture Window → Properties → PictureName → set dynamization to the tag.

5.2 Drive PictureName from a C action

// C action in TIA WinCC Professional
if (GetTagBit("ModeSelector") == 0)
{
    SetPropertyByTagName(lpszPictureName:="PictureWindow_1",
                         lpszPropertyName:="PictureName",
                         lpszValue:="Screen_Manual");
}
else
{
    SetPropertyByTagName(lpszPictureName:="PictureWindow_1",
                         lpszPropertyName:="PictureName",
                         lpszValue:="Screen_Automatic");
}

Refer to the SIMATIC WinCC Professional V17 Programming Manual for the full SetPropertyByTagName signature and supported property names.

6. Configuring the Trigger (Ctrl+I)

This is the part that catches every new WinCC scripter. Inside the C-Editor, every action has an Info dialog that controls execution frequency.

6.1 Open the trigger dialog

Use either:

• The action toolbar button Info/Trigger (in the action bar of the C-Editor), or
• Menu Edit → Info, or
• Keyboard shortcut Ctrl+I.

6.2 Trigger options

6.3 Recommended trigger for picture switching

Use a tag trigger on the mode tag with a 1-second standard cycle fallback enabled. This guarantees a periodic re-evaluation that catches any missed edge in case of bounce or lost trigger (e.g., after a tag gets its initial value when the runtime starts).

// Trigger configuration dialog (C-Editor Info / Ctrl+I)
//  Trigger:    @ModeSelector
//  Cycle:      1 s
//  Cold restart: TRUE

7. Multi-State Mode Selector (INT / WORD Tag)

A 1-bit mode selector is rarely enough. Real machines have Manual, Auto, Setup, Service, Cleaning and Fault modes. A single WORD tag plus a switch statement is cleaner than chained if/else.

// ac_ModePictureSwitch_Word.c
WORD wMode = GetTagWord("ModeSelector");

switch (wMode)
{
    case 0:  OpenPicture("Screen_Manual.pdl");    break;
    case 1:  OpenPicture("Screen_Automatic.pdl"); break;
    case 2:  OpenPicture("Screen_Setup.pdl");     break;
    case 3:  OpenPicture("Screen_Service.pdl");   break;
    case 4:  OpenPicture("Screen_Cleaning.pdl");  break;
    case 99: OpenPicture("Screen_Fault.pdl");     break;
    default: OpenPicture("Screen_Manual.pdl");    break;
}

8. Verification Procedure

After deployment, validate the script with this checklist:

1. Compile check. In the C-Editor, compile the action. The status bar must show 0 errors, 0 warnings. Warnings about implicit casts from WORD to int are common and harmless; warnings about undeclared identifiers are not.
2. Trigger visibility. Open Info/Trigger (Ctrl+I) and confirm the configured trigger tag and cycle are present.
3. WinCC diagnosis files. Activate the runtime, toggle the mode tag from the PLC or the WinCC tag simulator, and inspect WinCC_SStart_xx.log and APLOG*.txt in the WinCC project \Diagnostics\ folder.
4. Picture change confirmation. Watch the title bar / current picture name in Tools → Runtime Diagnostics → Picture Tree. The active PDL should change within one cycle after the tag flips.
5. Cold restart test. Stop the runtime, leave the mode tag at value 2, restart. The startup picture must be Screen_Setup.pdl, not the last-shown picture.

9. Troubleshooting Matrix

10. Performance and Safety Considerations

Picture-change actions are cheap, but in a 50,000-tag project with hundreds of actions the cumulative trigger load matters.

• Cycle cost. A 250 ms global action consumes roughly 0.5 % CPU per script on a typical WinCC server. Prefer tag triggers (edge-triggered) over tight cycles.
• Trigger granularity. One action with a multi-tag trigger beats ten single-tag actions. The runtime fires once when any listed tag changes.
• Auth gating. Picture change to a Service or Setup faceplate does not replace the authorization system. Apply User-Change visibility logic on top.
• Audit trail. Capture the mode tag in an archive so post-incident analysis can replay the picture transitions.
• Redundancy. On a redundant WinCC pair, replicate the C-Editor project by exporting/importing the entire script directory; do not copy single C files by hand.

11. Migration Notes: WinCC V7 → TIA WinCC Professional

When migrating, export global C actions from the V7 project, then import them in TIA via Scripts → Import/Export. Verify triggers, because the cycle dropdowns use slightly different default values between V7.4 and V17.

12. Frequently Asked Questions