WinCC I/O Field: Display INTEGER as Decimal REAL in TIA Portal

WinCC I/O Field: Display INTEGER as Decimal REAL in TIA Portal

1. Problem Overview

Field instrumentation and SIMATIC S7-1200/S7-1500 user programs frequently deliver process values as 16-bit or 32-bit integers where the least-significant digit already encodes the engineering resolution. A temperature transmitter scaled to 0.1 °C/count produces 1234 for 123.4 °C, a pressure transmitter produces 10132 for 1013.2 hPa, and a flow meter produces 1230 for 123.0 l/min. PLC programmers routinely guard the FB interface with INT or DINT tags because integer math is faster, deterministic, and avoids the 32-bit boundary issues that creep into REAL operations on S7-1200 firmware ≤ V4.2.

The operator, however, must read 123.4 °C, not 1234. Re-writing the PLC block to perform the divide-by-10 conversion is undesirable because:

• The PLC code is shared across multiple stations with different display conventions.
• Audit / validation of the safety-relevant FB must not be re-opened just to move a decimal point.
• The same raw integer is consumed by trending, archiving, and the SCADA layer where it must remain unscaled.
• PLC cycle time is reserved for I/O scanning, not display formatting.

This reference documents every supported method to render an INT/DINT/WORD process tag with a configurable decimal separator inside a WinCC I/O field, covering Basic Panels, Comfort Panels, RT Advanced, RT Professional, and WinCC Unified, on TIA Portal V14 SP1 through V20.

2. Prerequisites

3. Method 1 — Linear Scaling on the HMI Tag

The fastest method requires zero PLC change and keeps the HMI tag as an integer in the engineering view.

3.1 Procedure

1. In the TIA Portal project tree, expand HMI Tags and double-click the tag that is bound to the I/O field.
2. Switch to the Properties inspector and open Properties > Value (or the older "Scaling" group on V14 SP1).
3. Enable Linear scaling.
4. Set PLC end value and HMI end value such that the ratio produces the desired display range. Example for a 0–1000 PLC count mapped to 0–100.0 °C display:

   PLC start value : 0
   PLC end value   : 1000
   HMI start value : 0.0
   HMI end value   : 100.0

5. Compile and download the HMI station. The I/O field still binds an integer but the value bar and the formatted output use the scaled real range.

3.2 Limitations

• The HMI tag remains of type INT/DINT. Display is rounded unless the receiving I/O field adds a decimal place (see Method 3).
• Trends and archives store the raw integer, not the scaled real — verify downstream consumers.
• Linear scaling applies to value-bar / gauge widgets but does not produce a literal "12.3" string on its own.

4. Method 2 — Re-Type the HMI Tag as REAL

Switching the HMI tag data type forces the runtime to convert the integer to a 32-bit IEEE-754 float at the HMI boundary. No PLC change is required.

4.1 Procedure (TIA Portal V14 SP1 – V18)

1. Open the HMI tag editor.
2. Select the integer tag bound to the I/O field.
3. In the General column, change HMI Type from Int/DInt/Word to Real.
4. Confirm the connection. The PLC address is preserved; only the HMI-side representation changes.
5. Open the I/O field on the screen and set Format > Display format > Decimal (RT Advanced/Professional) or set Decimal places = 1 (Comfort Panels).
6. Compile and download.

4.2 Procedure (WinCC Unified, TIA Portal V16 – V20)

1. Open the Unified HMI tag editor and select the integer tag.
2. Under Properties, change Data type to Float32 (or the older synonym Real).
3. Open the screen and select the I/O field. In the Properties pane under Format, enable Decimal places and set DecimalPlaces = 1.

5. Method 3 — Comfort Panel "Decimal Places" Property

Comfort Panels (TP700, TP900, TP1200, TP1500, TP1900, TP2200) and Unified Comfort Panels (MTP series) expose a property that visually shifts the decimal separator inside an integer value without changing its type or its source. This is the cleanest answer for the original TIA V14 SP1 Professional scenario.

5.1 Procedure

1. Open the screen containing the I/O field.
2. Select the I/O field. In the Properties > General pane, scroll to Representation / Format.
3. Set Decimal places to the number of fractional digits you want to display (1 for "12.3", 2 for "1.23", etc.).
4. Verify the value in the simulation: a PLC value of 123 displays as 12.3 with one decimal place.
5. Compile and download to the panel.

5.2 Field-Proven Behaviour

• Range checking respects the original integer limits — a 16-bit signed integer still clamps at ±32 767.
• If the user enters "12.3" on the panel, the integer tag stores 123. The fractional part is preserved only on display; lossless round-trip is achieved.
• The decimal separator follows the project language (comma in DE/FR/IT, dot in EN/US). Use Project > Languages > Decimal separator to override.

6. Method 4 — Script + Scheduled Task (RT Professional / Unified)

When the I/O field sits on an RT Professional PC or a Unified PC runtime and no native decimal-places property is available, a tiny scheduled VBS / JavaScript converts the integer into an internal REAL.

6.1 RT Professional (VBScript)

' Scheduled task body - runs every 1000 ms
Dim iVal : iVal = SmartTags("Temp_RAW_INT")
SmartTags("Temp_HMI_REAL") = iVal / 10.0

6.2 Procedure

1. Create an internal HMI tag Temp_HMI_REAL of type Real.
2. Create a new scheduled task: RT Professional > Scheduled Tasks > Add new.
3. Set trigger = Cyclic, 1 s. Set action = VBScript action.
4. Paste the script from §6.1. Replace tag names with your project names.
5. Bind the I/O field to Temp_HMI_REAL instead of Temp_RAW_INT.
6. Set the I/O field Format property to Decimal with one decimal place (see §7).

6.3 WinCC Unified (JavaScript)

// Scheduled task - 1 s
let raw = Tags("Temp_RAW_INT").Read();
Tags("Temp_HMI_REAL").Write(raw / 10.0);

6.4 Why Schedule Rather Than a Direct Tag Formula?

Unified does not support tag-side expressions between an Int and a Real in a single step. The scheduled script is the lowest-overhead workaround and gives a deterministic 1 Hz update without flooding the tag log.

7. Method 5 — RT Professional I/O Field "Format" Property

The RT Professional runtime distinguishes decimal, binary, hexadecimal, date/time, and string output formats on the I/O field itself. Reference: I/O field: Format (RT Professional) — TIA Portal V20 documentation.

7.1 Procedure

1. Select the I/O field on the screen.
2. Open Properties > General > Format.
3. Set Output format = Decimal.
4. Set Display signed or unsigned depending on the integer range.
5. Bind the I/O field to a Real tag (Method 2) or to a script-scaled REAL tag (Method 4). Set Decimal places = 1.

7.2 Supported Format Tokens

8. Method 6 — WinCC Unified V19/V20 Integer-as-Decimal Procedure

Siemens Knowledge Base article 109816808 — WinCC Unified: Display integer value in an I/O field with decimal places documents the canonical Unified workflow.

1. Create (or reuse) a variable of type Integer — supported types are Int, DInt, Word, DWord, and the unsigned equivalents.
2. Place an I/O field on the screen and bind it to the integer variable.
3. Select the I/O field and open Properties > Format.
4. Enable Decimal places and choose how many fractional digits to render (1 for "12.3", 2 for "1.23", …).
5. Compile the HMI and start the Unified runtime. The integer is rendered with the configured separator at runtime.

9. Method Comparison

10. Verification Procedure

1. In TIA Portal, click Start simulation on the HMI station (or Online > Start Runtime for RT Professional).
2. Force the integer tag with the PLCSIM watch table to a known value (e.g., 1234).
3. Confirm the I/O field displays 123.4 with one decimal place and the comma/dot separator matches the project language.
4. Enter 567.8 in operator-input mode and read back the integer tag — it must hold 5678.
5. Trigger an out-of-range value (e.g., 65535 for a 16-bit tag with two decimals). Verify the field shows 655.35, not a wrap-around.
6. If using Method 4, open the scheduled-task log and confirm the script fired at the configured interval.

11. Troubleshooting Matrix

12. Frequently Asked Questions