Program Structure; Linear Programming - Siemens SIMATIC S5-90U System Manual

S5-90U/S5-95U
7.2

Program Structure

The programs of both PLCs can either be linear or structured.
Sections 7.2.1. and 7.2.2 describe these program types.
7.2.1

Linear Programming

Programming individual operations in one section (block) is sufficient for handling simple automation
jobs.
For the S5-90U and the S5-95U, this is organization block 1 (OB1) (see Section 7.3.1). The PLC
scans this block cyclically (i.e., after it scans the last statement, it goes back to the first statement
and begins scanning again).
Please note the following:
• Five words are assigned to the block header of OB1 in the program memory (see Section 7.3).
• Normally, a statement takes up one word in the program memory.
Two-word statements also exist (e.g., with the operation "Load a constant").
statements twice when calculating the program length.
• Like all blocks, OB1 must be terminated by a Block End statement (BE).
EWA 4NEB 812 6115-02b
Introduction to STEP 5
Count these
7-3