Page 358 - Programmable Logic Controllers, Fifth Edition - Mobile version

Optional
Optional
.Bit
Format Location :Slot :Type .Member .SubMember Optional
Local :2 :O .Data .4
Tag Name Data Type
Local:2:O.Data BOOL
Controller 01 23 4 56 7
Base tag memory 89 10 11 12 13 14 15
Local:2:O.Data.4 Tag data 16 17 18 19 20 21 22 23
24 25 26 27 28 29 30 31

Controller Scoped Tags

Figure 15-13 Base tag.

Fan_Motor Local:2:O.Data.5 Controller memory or consume the data. The producing controller will have
Alias tag Base tag Tag data a tag that is of the produced type, whereas the consuming
controllers will have a tag with the exact same name that
Fan_Motor is of the consumed type.
<Local:2:O.Data.5>
When you design your application, you configure it
to both produce globally to other controllers in the sys-
tem via the backplane and to consume tags from other
Figure 15-14 Alias tag linked to a base tag. controllers. This feature allows you to be selective about
which data are sent and received by any controller. Like-
wise, multiple controllers can connect to any data being
use of an alias tag. The alias tag (Fan_Motor) is linked to produced, thereby preventing the need to send multiple
the base tag (<local:2:O.Data.5>) so that any action to the messages containing the same data.
base also happens to the alias and vice versa. The alias Logix controllers are based on 32-bit operations. The
name is easier to understand and easier to relate to the ap- types of data that can be a base tag are BOOL, SINT,
plication, while the base tag contains the physical location INT, DINT, and REAL, as illustrated in Figure 15-16 and
of the output point in the ControlLogix chassis. listed below. The controller stores all data in a minimum
Produced/consumed tags are used to share tag informa- of 4 bytes or 32 bits of data.
tion over a network between two or more devices. A pro-
duced tag sends data while a consumed tag receives data. • A BOOL or Boolean base tag is 1 bit of data stored
Produced tags are always controller scoped. Figure 15-15 in bit 0 of a 4 byte memory location. The other bits,
shows an example of how a controller can produce data 1 to 31, are unused. BOOLs have a range of 0 to 1,
and send them over the network to two controllers that use off or on respectively.

Produced tag

Producer/consumer I/O model

Consumed tag
Logix5500
Input modules controllers Output modules

Network
Commonly shared data

Figure 15-15 Produced/consumed tags used to share information.
Source: Image Courtesy of Rockwell Automation, Inc.

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