Difference between shared symbols and local symbols - Database & Sql Blog Articles

The symbol makes it possible to work with a symbolic name with a meaning instead of an absolute address. Use short symbols and detailed comments to meet the requirements of effective program creation and good program documentation.

The differences between local symbols and local symbols are as follows:

Shared symbol local symbol validity

• Valid throughout the user program
• Can be used by all blocks
• Have the same meaning in all blocks
• The name in the entire user program must be unique

• Only valid in the block in which it is defined
• The same symbol can be used in different blocks depending on the application.

Allowed characters

• Letters, numbers, special characters
• Vowel symbols except 0x00, 0xFF and quotes
• When using special characters, the symbol must be in quotes

• letter
• digital
• Underlined ( _ )

Usage defines a shared symbol for:

• I/O signals (I, IB, IW, ID, Q, QB, QW, QD)
• Peripheral input/output (PI, PQ)
• Bit memory (M, MB, MW, MD)
• Timer (T) / Counter (Z)
• Code block (OB, FB, FC, SFB, SFC)
• Data block (DB)
• User-defined data type (UDT)
• Variable table (VAT)

Local symbols can be defined for:

• Block parameters (input, output, and input-output parameters)
• Block static data
• Block temporary data

Variable declaration table for defining point symbol table blocks

Precautions:
In code, shared symbols are identified by quotation marks ("..."), while local symbols are identified by a previous identifier (#). Identification is implemented automatically by STEP 7. However, if a symbol exists both as a shared symbol and as a local symbol, its identity must be clearly indicated to avoid confusion. In addition, this identifier is also required when using shared symbols that contain spaces.