Reading WinCC Flexible I/O Field Values in VBScript for Filenames

Overview

WinCC Flexible 2008 (and its successor, WinCC Comfort/Advanced inside TIA Portal) lets an engineer drive HMI behavior through VBScript attached to events on screens, buttons, value changes, and schedulers. A recurring task in this environment is reading the value the operator has just typed into an I/O Field and using it as the file name of a log, recipe export, alarm archive, or PDF report. The mechanism is identical whether the runtime is a SIMATIC Comfort Panel, a SIMATIC Basic Panel with scripting support, or a PC-based WinCC Runtime.

The runtime object model exposes the HMI tag behind the I/O Field through the SmartTags() function. Combining that value with a directory string and the Scripting.FileSystemObject COM object gives a complete, self-contained "operator-typed filename" workflow that does not require a custom DLL, an OPC bridge, or a separate archive application.

This reference covers the WinCC Flexible path end to end and provides the equivalent VBScript for the modern WinCC Unified V20 I/O Field object, because most field panels that shipped with WinCC Flexible 2008 SP5 are now being migrated to TIA Portal projects.

Prerequisites

Before the script can read a tag value and write a file, confirm the following prerequisites are met on both the engineering station and the runtime target.

• Engineering software. WinCC Flexible 2008 SP5 (legacy line) or TIA Portal V13 SP1 / V14 / V15 / V15.1 / V16 / V17 / V18 with WinCC Comfort or WinCC Advanced installed.
• Runtime target. A SIMATIC panel that supports VBScript: TP/OP/MP 277, TP/OP/MP 377, all Comfort Panels (TP700–TP2200, KP/KT), WinCC Runtime Advanced on a PC, or the modern Unified Comfort Panels (MTP/MTP Unified) for the WinCC Unified path.
• Project structure. At least one HMI tag, one screen, and one I/O Field configured on that screen.
• File system rights. For PC Runtime, write access to the chosen path (e.g. C:\Logs\, a USB stick mounted as \USB\ on a panel, or an SD card path). Panel runtimes write to the project path, the storage card path, or a USB stick plugged into the front USB.
• VBScript support enabled. In WinCC Flexible, VBScript is enabled per project by default on the panels listed above; legacy Basic Panels (KTP400 Basic mono) and the Micro Panel OP 73 / TP 177A do not support VBScript.

How the I/O Field Connects to a Tag

The I/O Field screen object is purely a view on a tag. It does not store its own data. When the operator types into the field, the runtime writes the value into the bound HMI tag; when a script reads the tag, it reads the same value the operator sees. The complete data path is therefore:

1. Engineer configures an HMI tag (e.g. Tag_string) of type String or WString.
2. Engineer drops an I/O Field on a screen and binds the Process / Variable property to Tag_string.
3. Runtime displays the current tag value inside the I/O Field.
4. Operator types a new value; runtime pushes the text into Tag_string.
5. Script reads Tag_string and uses it as a filename component.

Tag Configuration for Filename Use

Because the value is going to be part of a file path, the tag type and length must be chosen carefully. The table below summarises the settings that work in practice.

Binding the Tag to the I/O Field

1. In the project tree, open the screen and drop an I/O Field from the toolbox.
2. In the Properties > General dialog, set Mode to Input/Output (or Output if the script will set the value).
3. Click the Process / Variable property and select Tag_string from the tag browser.
4. Set Display type to String (not Decimal, Binary, etc.).
5. Set Length of the displayable value to match the tag length (e.g. 50).
6. Optionally, configure a Limit text in the Appearance tab and assign an Input finished event (used in the next step).

WinCC Flexible VBScript Object Model — SmartTags()

In WinCC Flexible, WinCC Comfort, and WinCC Advanced, the global SmartTags collection is the primary way to read or write a tag from VBScript. The collection behaves like a dictionary keyed by tag name and returns a variant containing the current value.

Dim v
v = SmartTags("Tag_string")  ' Read
SmartTags("Tag_string") = "NewValue"  ' Write

Key behaviours of SmartTags:

• It is implicitly available in every VBScript action — no Option Explicit declaration is required, and no CreateObject call is needed.
• The argument is a string literal matching the HMI tag name. Multilingual projects with a single tag across languages still use the engineering tag name.
• Reads are taken at script execution time, not at script edit time, so a subsequent SmartTags("Tag_string") access in the same script returns the live value.
• Writes are queued through the same runtime data manager used by the I/O Field, so the value updates in the screen as soon as the script returns.

Reading the I/O Field Value

Place the following VBScript on the Input finished event of the I/O Field, or on the Click event of a button next to the field. Both events fire after the runtime has accepted the operator input and committed it to the tag.

' --- WinCC Flexible / Comfort / Advanced VBScript ---
' Event: I/O Field "Tag_string" -> Input finished
' Purpose: read the typed value, compose a filename, and write a file.

Dim strBaseName
Dim strFullPath
Dim fso, ts

' 1. Read the value the operator just typed.
strBaseName = SmartTags("Tag_string")

' 2. Guard against an empty / null value.
If Len(strBaseName) = 0 Then
    SmartTags("Tag_string") = "Log"
    strBaseName = "Log"
End If

' 3. Compose the full path.
strFullPath = "C:\Logs\" & strBaseName & ".csv"

' 4. Create the file and write content.
Set fso = CreateObject("Scripting.FileSystemObject")
Set ts  = fso.CreateTextFile(strFullPath, True, True)   ' overwrite, Unicode
ts.WriteLine "Timestamp,Value"
ts.WriteLine Now() & ",0"
ts.Close

Set ts  = Nothing
Set fso = Nothing

The same script on a panel runtime must use a writable storage path. The conventional locations are:

• External storage card: \Storage Card\Logs\
• USB stick (Comfort Panels and Unified Panels): \USB\Logs\
• Network share (PC Runtime, RT Advanced): \\SERVER\Share\Logs\

Composing the Filename

The SmartTags value can be concatenated with fixed text, the current date, or other tags to form the final path. The most common patterns are shown below.

Sanitising the Filename

The most common runtime error when feeding a tag value to FileSystemObject is the operator typing a reserved character. A small helper function strips and replaces them:

Function SafeFileName(ByVal s)
    Dim i, ch, out
    Dim bad
    bad = Array("<", ">", ":", """", "/", "\\", "|", "?", "*")
    out = ""
    For i = 1 To Len(s)
        ch = Mid(s, i, 1)
        If InStr("<>:"/\|?*", ch) > 0 Then
            out = out & "_"
        ElseIf ch = Chr(32) Then
            out = out & "_"
        Else
            out = out & ch
        End If
    Next
    ' Trim trailing dot or space (Windows rule).
    Do While Right(out, 1) = "." Or Right(out, 1) = " "
        out = Left(out, Len(out) - 1)
    Loop
    If Len(out) = 0 Then out = "Log"
    SafeFileName = out
End Function

Use it before concatenating:

File System Operations with FileSystemObject

WinCC Flexible VBScript supports the standard Scripting library shipped with Windows. The two methods most often used together with an I/O Field value are:

' Ensure the target folder exists before writing.
Dim fso
Set fso = CreateObject("Scripting.FileSystemObject")
If Not fso.FolderExists("C:\Logs") Then
    fso.CreateFolder "C:\Logs"
End If

Complete Working Sample — Panel Runtime

The script below is bound to the Click event of a Save log button on a Comfort Panel screen. The I/O Field "FileNameIO" is bound to tag Tag_string.

' Event: Button "SaveLog" -> Click
' Panel: TP900 Comfort, WinCC Comfort V16
' Writes: \Storage Card\Logs\<operator_text>_<yyyymmdd>.csv

Dim fso, ts
Dim raw, safe, folder, full

raw  = SmartTags("Tag_string")
safe = SafeFileName(raw)

folder = "\Storage Card\Logs\"
full   = folder & safe & "_" & _
         Year(Now) & Right("0" & Month(Now),2) & Right("0" & Day(Now),2) & ".csv"

Set fso = CreateObject("Scripting.FileSystemObject")
If Not fso.FolderExists(folder) Then fso.CreateFolder folder

Set ts = fso.CreateTextFile(full, True, True)
ts.WriteLine "Tag,Value,Unit"
ts.WriteLine "Pressure," & CStr(SmartTags("Tag_pressure")) & ",bar"
ts.WriteLine "Flow,"     & CStr(SmartTags("Tag_flow"))     & ",l/min"
ts.Close

Set ts  = Nothing
Set fso = Nothing

' Show feedback in an I/O Field bound to Tag_status.
SmartTags("Tag_status") = "Saved: " & full

WinCC Unified V20 Equivalent

In WinCC Unified (TIA Portal V16 and later, currently V20), the SmartTags global is gone. Tags are read and written through the HMIRuntime object. The rest of the logic (String tag, I/O Field, FileSystemObject) is unchanged. The IO field (RT Unified) object behaves identically to the WinCC Flexible I/O Field: it shows the configured value in the chosen output format and, in input mode, writes operator text back to the bound tag.

' --- WinCC Unified V20 VBScript ---
' Event: Button "SaveLog" -> Click
' Bound tag: Tag_string (WString)

Dim fso, ts
Dim raw, safe, folder, full

raw  = HMIRuntime.Tags("Tag_string").Read()
safe = SafeFileName(CStr(raw))

folder = "\Storage Card\Logs\"
full   = folder & safe & "_" & _
         Year(Now) & Right("0" & Month(Now),2) & Right("0" & Day(Now),2) & ".csv"

Set fso = CreateObject("Scripting.FileSystemObject")
If Not fso.FolderExists(folder) Then fso.CreateFolder folder

Set ts = fso.CreateTextFile(full, True, True)
ts.WriteLine "Tag,Value,Unit"
ts.WriteLine "Pressure," & CStr(HMIRuntime.Tags("Tag_pressure").Read()) & ",bar"
ts.Close

Set ts  = Nothing
Set fso = Nothing

HMIRuntime.Tags("Tag_status").Write "Saved: " & full

Verification

After configuring the tag, the I/O Field, and the script, verify the chain in the order below.

1. Tag test. Open the tag table, monitor Tag_string, and confirm it updates as the operator types.
2. Script test (simulator). In the WinCC Flexible / Comfort / Advanced ES, run the project with the simulator. Click the button bound to the script and check the configured log path for a file with the typed name.
3. File system check. On the panel, open the file manager (where available) or, on a PC runtime, open Explorer at the target path and confirm the file exists with the expected size and encoding.
4. Empty-value check. Clear the I/O Field, press the button, and confirm the script falls back to a default name rather than raising an error.
5. Reserved-character check. Type a value such as Log/2026 and verify that the sanitiser replaces the slash.
6. Unified V20 path check. Repeat steps 1–5 against a Unified Panel or Unified PC Runtime if the project is being migrated.

Common Errors and Troubleshooting Matrix

Best Practices

• Sanitise before concatenating. Apply SafeFileName to every value coming from the operator; never trust screen input.
• Default value at runtime. Provide a sensible default (e.g. Log, Recipe01) so the script does not fail when the I/O Field is empty.
• Folder existence check. Wrap CreateTextFile with a FolderExists / CreateFolder pair to handle first-run and SD-card-swap cases on panels.
• Unicode mode. Open files in Unicode (CreateTextFile(path, overwrite, True)) to support German, French, Spanish, Chinese, and Cyrillic operator input.
• Path constants in one place. Define a single VBScript constant for the log folder and reuse it; the storage path differs between PC Runtime, panel runtime, and Unified panels.
• Status feedback tag. After saving, write the full path to a status I/O Field so the operator sees a confirmation on the same screen.
• Migration readiness. When porting a WinCC Flexible project to TIA Portal V16+ Unified, search and replace SmartTags( with the HMIRuntime.Tags(...).Read() / .Write() pattern; the I/O Field configuration and the FileSystemObject logic stay the same.
• Test on the real target. The simulator does not enforce panel write permissions; always validate on the actual device with the actual storage card or USB stick.

FAQ