Siemens NAN 67 Series Wartungshandbuch PDF herunterladen (Seite 48)

3-24

Ladder Logic (LAD) for S7-300 and S7-400

C79000-G7076-C504-02

3.12 Symbolic Addressing

In the Ladder programming language you can either enter absolute addresses,

parameters and block names, or use symbols. Using the menu command

View

Symbolic Representation, you can switch between symbolic and

absolute addressing.

To use shared symbols, you must enter them in the symbol table as follows:

S Open the symbol table with the menu command Options

Symbol

Table.

S Using the menu command Options

Edit Symbols open a dialog box in

which you can define and modify individual symbols.

For further information about editing symbols, refer to the User Manual

/231/.

In most cases it is not necessary to define whether a symbol is local or

shared. However, in cases where confusion might arise, for example if the

same symbol is being used in both the symbol table and the variable

declaration table, you can distinguish between the symbols as follows:

S Symbols from the symbol table are shown between inverted commas “..”.

S Symbols from the variable declaration table of the block are preceded by

the hash character “#”.

You do not enter the ID with “..” or “#” yourself. If the symbolic address is

contained in the variable declaration table or in the symbol table, the ID is

completed after the syntax check.

To make programming with symbolic addressing easier, you can display the

absolute address and symbol comment for a symbol. You display this

information with the menu command View

Symbol Information. If you

choose this option, a text box is displayed after each

network. You cannot

edit in this view. Any modifications you require must be made in the symbol

table or the variable declaration table.

Using Symbolic

Addressing

Specifying

Symbols

Representation

Symbol

Information

Made Easy

Creating Logic Blocks

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