Introducing the Global Data Service

The Global Data service in the 171 CBU 98091 processor provides an automatic data exchange for the coordination of PLC applications. Its key features include:

  • data exchanges based on a standard producer/consumer protocol, giving optimal performance while maintaining a minimum network load

  • real-time exchanges between stations in the same distribution group, which share variables used for PLC coordination

  • synchronization of remote applications

  • sharing of a common database among several distributed applications

Global Data Distribution Group

A Global Data distribution group consists of one or more stations on the same Ethernet subnet that exchange data variables. The following rules govern a Global Data variable distribution group:

  • A Global Data distribution group can consist of up to 64 stations.

  • A Global Data variable distribution group is identified by its Group Name, which is assigned in the Control Expert Data Editor.

  • There can be only one Global Data variable distribution group per logical IP subnet.

  • Each station in a variable distribution group operates on the same Class D IP multicast address with a configurable range of 224.0.0.0 through 239.255.255.255.

Global Data Variables

The following rules apply to the Global Data variable exchanged by stations in the distribution group:

  • A variable consists of a single block of contiguous words.

  • Each station can publish 1 variable consisting of up to 128 words.

  • Each station can subscribe to a maximum of 64 variables. However, if that station also publishes a variable, it can subscribe to a maximum of only 63 variables.

  • Each station can subscribe to any variable published by another station in the group.

  • Each station has a maximum subscription of 2,048 total words.

Global Data Tab

To access the configuration parameters on the Global Data tab:

Step

Action

1

In the Project Browser, navigate to the Communication > Networks subdirectory.

2

Double-click the appropriate Ethernet network to open its configuration dialog.

3

In the Module Utilities field, select Yes in the Global Data menu.

4

Select the Global Data tab:

5

In accordance with your system and application needs, elect and assign the Global Data configuration parameters, as described below.

6

Configure variables for the Global Data service. (see below)

Global Data Configuration Parameters

The following parameters can be set in the Global data configuration area on the Global Data tab:

Parameter

Description

Health time out

Use this field to set the time-out value: from 50...15 000 ms in increments of 50 ms. Default = 200 ms.

Group address

Use this to identify the multicast IP address (class D) of the distribution group to which the station belongs:

  • minimum value: 224.0.0.0

  • maximum value: 239.255.255.255 (Default)

Distribution period

Use this field to set the frequency of the publication. The value is multiplied by 10 ms to determine the time between updates. The minimum value is 2, yielding a minimum frequency of 20 ms.

Group name

Input the name that associates a variable from the Data Editor with a module. Each group name is created in the Control Expert Data Editor.

Multicast filtering

Use this check box to turn multicast filtering ON and OFF. Values include:

  • None: Disables GRMP. Data will be sent to each end device in the network. (Default)

  • GRMP: Enables GRMP (general router management protocol).

NOTE: Filtering can reduce data flow on large networks. Multicast filtering requires the use of switches and routers that support the selected protocol.

Health bit block

Input the address for the first word – of 4 contiguous words – that store health data for the stations that comprise the Global Data distribution group. Default = %MW9.

Each bit in the sequence of words starting at this address indicates the health of an associated station. A bit value of:

  • 1 = successful publication or subscription

  • 0 = the Health time out period elapsed before completion of the publication or subscription

Configure Global Data Variables

Global Data variables are configured in the Data Editor:

Step

Action

1

In the Control Expert main menu, select View > Structural View to display that view of the project in the Project Browser.

2

Navigate to and double-click Variables and FB Instances:

The Data Editor table (displayed in step 5, below) appears.

NOTE: The Data Editor does not yet display the Global data column.

3

Right-click in the first row in the Data Editor, and select Customize Columns from the menu.

The Customize Columns window appears:

4

In the Customize Columns... dialog, select the Global Data check box, and press OK.

5

The Data Editor now displays the Global data column:

6

In the Global data column, select one of the following for each variable:

  • NO: not published and not subscribed

  • PUB: published

  • SUB: subscribed

7

Associate each Global Data item with a group name in the Group column.

8

Enter the identifier of a remote station in a distribution group in the ID column.