Page 368 - Programmable Logic Controllers, Fifth Edition - Mobile version

With text-based Logix systems you can use the name
of the tag to document your ladder code and organize New Tag
your data to mirror your application. For the programmed Name: Motor_Start
motor start/stop control circuit three tags, Motor_Start, Description: Start button for
Motor_Stop, and Motor_Run, are created. Figure 15-33 motor
illustrates how the Motor_Start tag is created in the New
Tag window. This window can be accessed by right Alias
clicking the ? mark above the XIC instruction in the lad- Local:1:I.Data
der logic program. Since this tag represents a value from Name Data Type
an input field device, a link through the module to the + Local:1:C AB:1756_DO:C:0
field device must be created. When Local:1:I.Data is se- – Local:1:I AB:1756_DO:I:0
lected a dialog box for all of the terminal numbers on the Local:1:I.Fault DINT
input module appears. The tag name (Motor_Start) used Local:1:I.Data
in the program is then linked to input terminal number 3 0 1 2 3 4 5 6 7
9 10 11 12
8
where the field device represented by the tag name is 16 17 18 19 20 13 14 15
21 22 23
connected. 24 25 26 27 28 29 30 31
Figure 15-34 shows what the ladder logic program
would look like after all three tags have been created. Figure 15-33 Creating the Motor_Start tag.
Users have the ability to reference data via multiple names Source: Image Courtesy of Rockwell Automation, Inc.
using Aliases. This allows the flexibility to name data dif- but the description is not, as it is part of the documenta-
ferently depending on their use. The tag description pro- tion of the project.
vides for a more meaningful description of the tag name. Figure 15-35 shows the state of the tags created for
Tag names are downloaded and stored in the controller the motor start/stop program as seen in the program and

Description Start button for Stop button for
motor motor Motor contactor coil
Tag Name Motor_Start Motor_Stop Motor_Run
Alias <Local:1:I.Data.3> <Local:1:I.Data.4> <Local:2:O.Data.4>

Motor contactor coil
Motor_Run
<Local:2:O.Data.4>

Figure 15-34 Ladder logic program after all tags have been created.

Inputs Ladder logic program Output
Start button for Stop button for
L1 motor motor Motor contactor coil L2
Motor_Start Motor_Stop Motor_Run
<Local:1:I.Data.3> <Local:1:I.Data.4> <Local:2:O.Data.4>
Motor_Stop Motor_Run M

Motor contactor coil
Motor_Start Motor_Run
<Local:2:O.Data.4>
Stop
Contactor
Start Monitor Tags Window

Tag Name Value Style Data Type Description
Motor_Start 0 Decimal BOOL Start button for motor
Motor_Stop 1 Decimal BOOL Stop button for motor
Motor_Run 1 Decimal BOOL Motor contactor coil
Figure 15-35 Ladder logic program and Monitor Tags window with motor operating.

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