63Publication 1756-PM004C-EN-P - October 2009 63
Chapter
4
Data Access Control
Introduction
In the Logix platform, software version 18 or later, 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 a tag can be modified by controller
logic. Also, by using FactoryTalk Security software, it is possible to control
which users are permitted to change tags designated as constants in
RSLogix 5000 software. See
page 79
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 also reduce the time required to develop
HMI screens.
External Access
By using the External Access attribute, you can control how external
applications and devices can access tags.
This process can help you manage the thousands of tags you might have in a
project that have similar names that can get easily confused when referencing
them in applications or devices.
Using this attribute also can help improve system performance by reducing the
number of tags RSLinx has to maintain, scan, and cache. This volume can
impact 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.
• FactoryTalk Historian software.
• other third-party software.
To Next Page
Loading...
Need help?
General
