Displaying Text on Siemens HMI from PLC Tag Values (TIA Portal)

1. Problem Statement and Use Case

Many HMIs must translate a small set of numeric state indices coming from the PLC into a human-readable text label. A typical example: a machine exposes a single INT tag called ModeIndex with values 0..4, and the operator must see PARALLEL, SERIAL, SHUNTED, KILLED, or ALIVE on the screen, plus change the color of the indicator accordingly. Building six overlapping text boxes with visibility animation works but is fragile, language-locked, and painful to maintain.

Siemens TIA Portal / WinCC provides a first-class object for exactly this pattern: the Text list. Combined with a Symbolic I/O field, one HMI tag drives the entire text and color chain. This article shows every working method, the trade-offs, the PLC code required to set the index, and the panel-level limits you must respect when commissioning.

2. Prerequisites

3. Method 1 - Text List with Symbolic I/O Field (Recommended)

This is the canonical Siemens pattern. One HMI tag drives one text list, and the Symbolic I/O field renders the entry that matches the current value.

3.1 Create the HMI tag

1. In the TIA Portal project tree, open HMI Tags → double-click Default tag table (or your custom table).
2. Add a new tag, e.g. ModeIndex, of data type Int.
3. Set the Connection to the S7 PLC, leave the address in symbolic form if your PLC uses symbolic tags, or enter the absolute address, e.g. %DB5.DBW0 for a data block word.
4. Acquisition cycle: 1 s is fine for a mode display; raise to 100 ms if the index toggles during hand-shake transitions.

3.2 Create the Text List

1. In the project tree, expand HMI → Text and graphics lists → double-click Text lists.
2. Click Add new, name it e.g. ModeList.
3. Set the List range to Bit (0/1) for boolean fields or Value/Range for integer states. For 0..4 you must use Value/Range.
4. Set Default entry (shown when the tag value is out of range) - typically ??? or INVALID.
5. Populate the entries as in the table below.

Each row can carry a background and foreground color. The color is selectable from the list editor; it is consumed by the Appearance dynamization of any object that is linked to the text list.

3.3 Place a Symbolic I/O Field on the screen

1. Open the desired screen, drag a Symbolic I/O field from the toolbox onto the canvas.
2. In the properties → General, set:
   • Mode = Output (read-only) or Input/Output if the operator can change mode from this field.
   • Tag = ModeIndex (HMI tag).
   • Text list = ModeList.
3. Configure the field: appearance, font, border, and field length so the longest entry fits (count characters including the longest word in the active language).

At runtime the Symbolic I/O field now shows PARALLEL when the PLC writes 0, SERIAL when it writes 1, and so on. If the operator clicks the field, an input popup opens listing all values so the operator can select one - WinCC writes the chosen value back to the PLC tag.

3.4 Why this is the right answer

• One tag, one object - no per-state text boxes, no overlapping z-order issues.
• Multi-language - each list entry stores up to 32 languages. Switching the HMI runtime language on the panel updates the field automatically.
• Consistent colors - colors are part of the list entry, so multiple screens referencing the same list are visually identical.
• Audit-friendly - operators can pick the mode from a list, no risk of typing 2 when they meant 20.

4. Method 2 - Pure Read-Only Text Field with a String Tag

If you want absolute control over the displayed text - including dynamic concatenation with other values - skip the text list and let the PLC build the final string.

4.1 PLC side (SCL, S7-1500)

// FB "ModeTextBuilder"
CASE #iMode OF
    0: #sModeText := 'PARALLEL';
    1: #sModeText := 'SERIAL';
    2: #sModeText := 'SHUNTED';
    3: #sModeText := 'KILLED';
    ELSE
        #sModeText := 'ALIVE';
END_CASE;

// Optional: append live diagnostics
#sModeText := CONCAT(STRING_TO_WSTRING(#sModeText),
                      WSTRING#'  I=' + INT_TO_WSTRING(#iCurrent));

4.2 HMI side

1. Create a tag ModeText of type WString[254] (WString is required for Unicode and is the default on TIA V17+).
2. Place an I/O field in Output mode and assign the ModeText tag.
3. Set Output format to String and disable input.

5. Method 3 - Color and Visibility Animation per State

When a text list is unavailable (e.g. Basic Panel) or you need extra graphical effects (icon swap, blinking), you can still animate a Rectangle or Symbolic I/O field through a Tag-based or PLC-controlled animation.

5.1 Color dynamization on a Symbolic I/O field

1. Select the field, open Properties → Appearance → Background color.
2. Click the small dynamization icon and add an PLC-controlled animation with up to 10 ranges:

5.2 Visibility of stacked labels

For a 5-state panel, place five text boxes (one per state), each with a visibility animation on the same ModeIndex tag:

• Text "PARALLEL" visible when 0 ≤ ModeIndex ≤ 0
• Text "SERIAL" visible when 1 ≤ ModeIndex ≤ 1
• ... and so on.

6. Method 4 - Tag Value Inside Alarm / Event Text

When the requirement is "show the current mode inside an alarm line" rather than on a screen, TIA Portal lets you embed a tag value as a placeholder in the alarm text. Siemens documents this workflow in the official support entry How do you output a tag value in the alarm text on WinCC (TIA Portal)? The procedure is:

1. Open HMI alarms → Discrete alarms (or Analog alarms) and create the alarm.
2. Place the cursor in the Event text at the position where the mode should appear.
3. Right-click → Insert tag output field.
4. Pick the ModeIndex tag, choose the format (Decimal for the raw value, Text + text list ModeList for the human label).

The alarm line then prints, e.g., "Unit switched to PARALLEL (index=0) at 12:43:07". This is invaluable for diagnostics, logbook export, and trending.

7. Driving the Index Tag from the PLC

All four methods above require that the PLC writes a valid integer to ModeIndex. The cleanest pattern is an FB that owns the mode transitions and exposes one ModeIndex output to the HMI tag table.

7.1 SCL implementation (S7-1500)

FUNCTION_BLOCK "FB_ModeController"
VAR
    bInit : BOOL := TRUE;
END_VAR
BEGIN
    // Latch mode on rising edge of the source flags
    IF #bParallel AND (#iMode <> 0) THEN
        #iMode := 0;                     // PARALLEL
    ELSIF #bSerial AND (#iMode <> 1) THEN
        #iMode := 1;                     // SERIAL
    ELSIF #bShunted AND (#iMode <> 2) THEN
        #iMode := 2;                     // SHUNTED
    ELSIF #bKilled AND (#iMode <> 3) THEN
        #iMode := 3;                     // KILLED
    ELSIF (#iMode <> 4) THEN
        #iMode := 4;                     // ALIVE (default / no trip)
    END_IF;

    // Output mirrors the index for HMI polling
    #iModeIndex := #iMode;
END_FUNCTION_BLOCK

7.2 Ladder (FBD/ST) equivalent

      |  bParallel  iMode<>0  |
--| |------|/|---------( S )--  iMode := 0    (PARALLEL)
      |  bSerial    iMode<>1  |
--| |------|/|---------( S )--  iMode := 1    (SERIAL)
      |  bShunted   iMode<>2  |
--| |------|/|---------( S )--  iMode := 2    (SHUNTED)
      |  bKilled    iMode<>3  |
--| |------|/|---------( S )--  iMode := 3    (KILLED)

7.3 Resetting on operator action

If the operator selects a new mode from the Symbolic I/O field, the runtime writes the chosen Int back to the PLC tag. Ensure the PLC uses that value as the new authoritative state, e.g. by adding a cyclic move from the HMI tag to the controller's mode variable:

// Cyclic OB1
"DB_Mode".iMode := "HMI".ModeIndex;

8. Multi-Language Text Lists

WinCC supports up to 32 project languages. For a text list:

1. Open Project → Languages → Add language and pick the target language (e.g., German, French).
2. Open the text list ModeList - a column appears for each language.
3. Translate each row. The PLC tag is language-agnostic, only the displayed string changes.
4. Set the Runtime language on the panel in Control Panel → Language or programmatically via the SetLanguage system function.

Symbolic I/O fields, alarm text, and event text all consume the same text list entry, so a single translation effort updates the entire HMI. See the TIA Portal help section Working with multi-language projects for a list of supported export formats (XLIFF, CSV) used for translator round-trips.

9. Limits, Performance, and Licensing

For WinCC Professional / WinCC RT PC you can also bind a text list directly to a DB field using the new WinCC Unified scripting API (HMIRuntime.Tags), but the principle - integer value drives text and color - stays the same.

10. Verification and Commissioning

1. Compile the HMI project (TIA Portal → right-click HMI device → Compile). Zero warnings expected.
2. Start the simulator (Start runtime) and, in PLCSIM, force ModeIndex to 0..4 in turn. Confirm the field updates within one acquisition cycle.
3. Force a value outside the list range (e.g. 99). Confirm the Default entry appears - this proves the fallback is wired correctly.
4. Change the panel runtime language to German and verify the second-language column is rendered.
5. Click the Symbolic I/O field, select a different value from the popup, and confirm the PLC tag is written back. Trace with a watch table.
6. Cycle power to the panel; confirm the value is re-read from the PLC at startup, not retained locally (HMI tags have configurable Retain behavior - disable for mode index).

11. Troubleshooting Matrix

12. Comparison of Methods

For the use case of one PLC integer driving one operator label, Method 1 (Text list + Symbolic I/O field) wins on every axis. Reach for Method 2 only when the displayed text must embed other live data, and for Method 3 only when the panel cannot be upgraded from a Basic to a Comfort target.