Siemens ET 7Y Series Especificaciones descargar pdf (Pagina 133)

Functions of the IM 151-7 CPU

8-21

ET 200S IM 151-7 CPU Interface Module

A5E00058783-04

Process image of the inputs and outputs

If the address areas ”inputs” (I) and ”outputs” (O) are addressed in the user

program, the signal states on the digital electronic modules are not checked, but

instead a memory area in the system memory of the CPU is accessed. This

memory area is referred to as the process image.

The process image is divided into two parts: the process image of the inputs and

the process image of the outputs.

Advantages of the process image

The advantage of accessing the process image over accessing the electronic

modules directly is that a consistent image of the process signals is available to the

CPU for the duration of cyclic program processing. If a signal state at an input

module changes during program processing, the signal state is retained in the

process image until the process image is updated in the next cycle. Furthermore,

accessing the process image requires much less time than accessing the

electronic modules directly because the process image is located in the system

memory of the CPU.

Updating the process image

The process image is updated by the operating system cyclically. The figure below

shows the processing steps within a cycle.

Startup program

Writing the process image of the outputs

to the electronic modules

Reading the inputs from the electronic modules and

updating the data in the process image of the

inputs

Processing the user program (OB 1 and

all blocks called in the program)

Startup

PIQ

PII

User program

CCP (OpSy)

Cycle time

Figure 8-5 Processing steps within a cycle

1 2 ... 128 129 130 131 132 133 134 135 136 137 138 ... 213 214

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Siemens ET 7Y Series Especificaciones Pagina 133