Siemens S7-400PLC Dokumentacja Pobierz pdf (Strona 463)

Glossary

S7-400 Automation System Module Data

Reference Manual, Edition 09/2009, A5E00850736-06

463

Operating state

The automation systems of SIMATIC S7 recognize the following operating modes or simply

modes: STOP, → STARTUP, RUN and HOLD.

Operational limit

The operational limit is the measurement or output error of the analog module throughout the

entire temperature range related to the nominal range of the analog module.

Parameters

1. Variables of a → logic block

2. Variable for setting the properties of a module (one or more per module). When shipped,

every module has practical basic parameter settings that the user can modify in STEP 7.

Point-to-point link

On a point-to-point link, only two nodes are physically linked to each other. This type of

communications link is used when the use of a communication network is not practical or

when different types of nodes need to be connected (for example, PLC with process

computer).

Priority class

The S7 CPU operating system provides up to 28 priority classes (= program execution

levels"), for example for cyclic program execution, hardware interrupt-controlled program

execution.

Each priority class is assigned to → organization blocks in which the user can program a

reaction. The OBs have different default priorities and if the OBs are called at the same time,

the priority decides which executes first and which can interrupt another. The default

priorities can be modified by the user.

Process image

The signal states of the digital input and output modules are entered in a process image on

the CPU.

A distinction is made between the process image of the inputs and the outputs. The process

image of the inputs (PII) is read from the input modules by the operating system prior to

execution of the user program. The process image of the outputs (PIQ) is transferred to the

output modules by the operating system on completion of program execution.

Product version

The product version distinguishes products with the same order number. The product

version is incremented when upwards-compatible functional enhancements are made, when

there are modifications relating solely to production (use of new components) and when

bugs are fixed.

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Siemens S7-400PLC Dokumentacja Strona 463