PLC Steps – Your Guide to Industrial Automation

Common Data Types in TIA Portal

TIA Portalsupports a wide variety of data types used to represent values, signals, states, timers, characters, and structured data. Below are the most frequently used types when programming OBs, FCs, FBs, and DBs.

BOOL

• Represents a binary value: TRUE or FALSE.
• Typically used for digitalsignals, flags, and conditions.

INT / UINT

• INT: 16-bit signed integer → Range: -32,768 to +32,767
• UINT: 16-bit unsigned integer → Range: 0 to 65,535
• Used for counters, timers, small numeric values.

DINT / UDINT

• DINT: 32-bit signed integer → Range: -2,147,483,648 to +2,147,483,647
• UDINT: 32-bit unsigned → Range: 0 to 4,294,967,295
• Used when larger numerical range is needed (e.g., encoder values, runtime logs).

REAL / LREAL

• REAL: 32-bit floating point number (approx. 7 decimal digits precision)
• LREAL: 64-bit floating point number (higher precision, approx. 15-17 digits)
• Used for analog signals, scaling, calculations with decimals.

BYTE

• 8-bit data type. Can be used for grouping 8 BOOLs or storing raw values.
• Often used for communication buffers or binary flags.

CHAR

• Stores a single ASCII character (1 byte).

STRING / WSTRING

• STRING: A series of ASCII characters (up to 254 characters).
• WSTRING: Wide-character string (for Unicode/UTF-16 support), typically used in multilingual or HMI applications.

TIME

• Stores time values (e.g., T#5s, T#1h30m10s).
• Used for timers, delays, or timestamping.

ARRAY [x..y] OF <type>

• Collection of elements of the same type, indexed by position.
• Example: ARRAY [1..5] OF INT stores 5 integer values.
• Commonly used for sensor arrays, batch data, or buffer management.

Variable Interface Types(Declaration Sections)

Each block type (FC, FB, OB) in TIA Portal allows you to declare variables in different interface sections, each serving a specific purpose in terms of data flow and memory usage.

Input (IN)

• Read-only from inside the block.
• Values are passed from the calling block to the function or function block.
• Cannot be modified inside the block.

Example: A temperature setpoint passed into a heating control FB.

Output (OUT)

• Write-only from inside the block.
• Used to send data back to the caller.
• Must be assigned a value within the block to be meaningful.

Example: An error flag that indicates fault status to the calling OB.

InOut

• Allows the block to both read and modify the same variable.
• Changes are reflected back to the caller.
• Used with caution — potential for unexpected side effects.

Example: A cumulative runtime counter that is updated in each scan.

Temp

• Temporary variables, stored in the local stack of the block.
• Exist only during block execution and are not retained.
• Cannot be accessed outside the block.
• Ideal for intermediate calculations orstate tracking that doesn’t need to persist.

Example: A temporary result in a math formula inside an FC.

Summary Table

Data Type	Description	Typical Use
BOOL	TRUE / FALSE	Digital I/O, flags
INT , DINT	Signed integers	Counters, value
REAL , LREAL	Floating point	Analog values, scaling
BYTE	8 bits	Grouped bits, comms
CHAR ,STRING, WSTRING	Text data	HMI, logging
TIME	Time format	Timers, delays
ARRAY [x,y] OF …	Indexed list	Buffers,sensor groups

Variable Type	Direction	Scope	Persistence
Input	IN	From caller → block	Read-only
Output	OUT	From block → caller	Write-only
InOut	Both	Shared	Read/Write
Temp	Internal	Local Only	Lost after execution

Example of Variables Declaration

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