Data access control, Introduction, External access – Rockwell Automation Logix5000 Controllers I/O and Tag Data Programming Manual User Manual
Page 63: Chapter 4, Introduction external access
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
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
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
Rock well Automati on Publication 1756- PM004E -EN-P - October 2014
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