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Glossary-5

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

C79000-G7076-C504-02

When a block is input incrementally, each line or element is checked

immediately for errors (for example syntax errors). If an error is detected, it

is marked and must be corrected before programming is completed.

Incremental input is possible in STL (Statement List), LAD (Ladder Logic),

and FBD (Function Block Diagram).

An “instance” is the call of a function block. If, for example, a function is

called five times in a STEP 7, then there are five instances. Each call is

assigned to an instance data block.

An instance data block stores the formal parameters and the static local data

of function blocks. An instance data block can be assigned to one or more

function blocks.

An instruction is part of a statement; it specifies what the processor should

do.

Key words are used when programming with source files to identify the start

and end of a block and to select sections in the declaration section of blocks,

the start of block comments and the start of titles.

Ladder Logic is a graphic programming language in STEP 5 and STEP 7. Its

representation is standardized in compliance with DIN 19239 (international

standard IEC 1131-1). Ladder Logic representation corresponds to the

representation of relay ladder logic diagrams. In contrast to Statement List

(STL), LAD has a restricted set of instructions. In STEP 5, this language is

known as Ladder Diagram.

Logic blocks are the blocks within STEP 7 that contain the program for the

control logic. In contrast, data blocks (DBs) only contain data. There are the

following types of logic blocks: organization blocks (OBs), functions (FCs),

function blocks (FBs), system functions (SFCs), and system function blocks

(SFBs).

Input, Incremental

Instance

Instance Data

Block (DB)

Instruction

Key Word

Ladder Logic

(LAD)

Logic Block

Glossary

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Siemens NAN 67 Series Wartungshandbuch Seite 299