Siemens S7-300 appendix Cycle time, Overview, Meaning of the term cycle time, Time slice model

Cycle and reaction times 5.2 Cycle time

5.2Cycle time

5.2.1Overview

Introduction

This section explains what we mean by the term "cycle time", what it consists of, and how you can calculate it.

Meaning of the term cycle time

The cycle time represents the time that an operating system needs to execute a program, that is, one OB 1 cycle, including all program sections and system activities interrupting this cycle. This time is monitored.

Time slice model

Cyclic program processing, and therefore user program execution, is based on time shares. To clarify these processes, let us assume that every time share has a length of precisely

1 ms.

Process image

During cyclic program processing, the CPU requires a consistent image of the process signals. To ensure this, the process signals are read/written prior to program execution. Subsequently, the CPU does not address input (I) and output (Q) address areas directly at the signal modules, but rather accesses the system memory area containing the I/O process image.

5-2	CPU 31xC and CPU 31x, Technical data
	Manual, Edition 08/2004, A5E00105475-05