Rockwell-automation Logix5000 Controllers I/O and Tag Data Programming Instrukcja Użytkownika Pobierz pdf (Strona 63)

Chapter 4

Data access control

In version 18 or later of the Logix Designer application, there are two tag

attributes that allow you to control access to tag data. These attributes are:

• External Access

• Constant

The External Access attribute controls how external applications, such as HMIs,

can access tags. It has possible values of Read/Write, Read Only, and None. See

Configure external access on page 64

The Constant attribute value determines if controller logic can change a tag. Also,

by using FactoryTalk Security software, it is possible to control which users can

change tags designated as constants in the Logix Designer application. See

Constant value tags on page 76

for more information on the Constant attribute.

By using these two attributes, you can help safeguard tag data by preventing

unwanted changes to tag values. Also, by reducing the number of tags exposed to

external applications, you can reduce the time required to develop

HMI screens.

You can control how external applications and devices can access tags by using the

External Access attribute.

Using external access reduces the number of tags for an application that appear

when you reference them in applications or devices. It can also improve system

performance by reducing the number of tags RSLinx has to maintain, scan, and

cache. Reducing the number of externally accessible tags can improve the

performance of the RSLinx data server and other related applications.

External applications and devices include:

• RSLinx Classic and RSLinx Enterprise software.

• Other Logix controllers.

• PanelView terminals.

• PLC/SLC controllers.

Introduction

External access

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Rockwell-automation Logix5000 Controllers I/O and Tag Data Programming Instrukcja Użytkownika Strona 63