Tag-Based Addressing Logix 5000 controllers use a tag-based addressing structure. A tag is a text-based name for an area of the controller where data is stored. An example of how a tag-based address is implemented using a ControlLogix controller is shown in Figure 15-30. Tag names use a meaningful description of the variable. In this application when the normally closed high limit switch is activated the program will switch the high limit output light on. The addressing format can be summarized as follows: • The physical address for the tag Limit_switch is Local:1:I.Data.2(C). Local indicates that the module is in the same rack as the processor, 1 indicates that the module is in slot 1 in the rack, I indicates that the module is an input type, Data indicates that it is a digital input, 2 indicates that the limit switch is connected to terminal 2 on the module, and C indicates that it is a controller tag with global access. • The physical address for the tag High_limit_light is Local:2:O.Data.4(C). Local indicates that the module is in the same rack as the processor, 2 indicates that the module is in slot 2 in the rack, O indicates that the module is an output type, Data indicates that it is a digital input, 4 indicates that the high limit light is connected to terminal 4 on the module, and C indicates that it is a controller tag with global access. One advantage of the use of tag-based addressing is that the allocation of variable names for program values is not tied to specific memory locations in the memory structure, as is the case with rack/slot and rack/group type systems. Alias For Local:1:I.data.2(C) Local:2:O.data.4(C) Limit_switch Switch - closed Processor module Power supply TAG EDIT 0 Base Tag Local:1:I.data.2(C) Local:2:O.data.4(C) High_limit_light Light-OFF 1 2 3 4 5 6 Tag Name Limit_switch High_limit_light 8-point discrete (digital) input module Program 0 1 2 3 4 5 6 7 Limit_switch <Local:1:I.data.2(C)> Value 1 0 TAG MONITOR Tag Name Limit_switch High_limit_light Figure 15-30 Tag-based address implementation. Type BOOL BOOL 7-slot ControlLogix chassis Style Decimal Decimal 8-point discrete (digital) onput module 0 1 2 3 4 5 6 7 High_limit_light <Local:2:O.data.4(C)> Style Decimal Decimal Type BOOL BOOL Bit-Level Programming Part 2 347
Petruzella_ProgrammableLogicControllers__5e
To see the actual publication please follow the link above