Optional Format Location :Slot :Type .Member .SubMember .Bit Base tag Local :2 :O .Data .4 Local:2:O.Data.4 Tag data Figure 15-13 Base tag. Controller memory Fan_Motor Local:2:O.Data.5 Controller memory Alias tag Base tag Tag data Fan_Motor <Local:2:O.Data.5> Figure 15-14 Alias tag linked to a base tag. use of an alias tag. The alias tag (Fan_Motor) is linked to the base tag (<local:2:O.Data.5>) so that any action to the base also happens to the alias and vice versa. The alias name is easier to understand and easier to relate to the application, while the base tag contains the physical location of the output point in the ControlLogix chassis. Produced/consumed tags are used to share tag information over a network between two or more devices. A produced tag sends data while a consumed tag receives data. Produced tags are always controller scoped. Figure 15-15 shows an example of how a controller can produce data and send them over the network to two controllers that use Optional Tag Name Data Type Local:2:O.Data BOOL 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 Controller Scoped Tags or consume the data. The producing controller will have a tag that is of the produced type, whereas the consuming controllers will have a tag with the exact same name that is of the consumed type. When you design your application, you configure it to both produce globally to other controllers in the system via the backplane and to consume tags from other controllers. This feature allows you to be selective about which data are sent and received by any controller. Likewise, multiple controllers can connect to any data being produced, thereby preventing the need to send multiple messages containing the same data. Logix controllers are based on 32-bit operations. The types of data that can be a base tag are BOOL, SINT, INT, DINT, and REAL, as illustrated in Figure 15-16 and listed below. The controller stores all data in a minimum of 4 bytes or 32 bits of data. • A BOOL or Boolean base tag is 1 bit of data stored in bit 0 of a 4 byte memory location. The other bits, 1 to 31, are unused. BOOLs have a range of 0 to 1, off or on respectively. Consumed tag Produced tag Network Figure 15-15 Produced/consumed tags used to share information. Source: Image Courtesy of Rockwell Automation, Inc. Producer/consumer I/O model Logix5500 Output modules controllers Input modules Commonly shared data Memory and Project Organization Part 1 339
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