Page 356 - Programmable Logic Controllers, Fifth Edition - Mobile version

Main Task programming language. When a routine is created it is
specified as ladder logic, sequential function chart, func-
Main Program tion block diagram, or structured text (Figure 15-9). Any
Program_A one routine must be completely in the same language.
Program_B
The number of routines per project is limited only by the
Unscheduled Programs
amount of controller memory. Libraries of standard rou-
Figure 15-8 Order of execution of programs. tines can be created that can be reused on multiple ma-
chines or applications. A routine can be assigned as one
of the following types:
execute. There is no executable code within a program.
Routines within programs will execute in the order listed • A main routine is one configured to execute first
below their associated task in the controller organizer as when the program runs. Each program will have one
shown in Figure 15-8. In this example, according to the main routine typically followed by several or many
listed order, the Main Program is scheduled to execute subroutines.
first, Program_A second, and Progam_B third. Programs • A subroutine is one that is called by another rou-
that are not assigned to a task are unscheduled. Unsched- tine. Subroutines are used for large or complex pro-
uled programs are downloaded to the controller but do gramming tasks or tasks that require more than one
not execute. These programs remain unscheduled until programming language.
needed. Depending on the RSLogix 5000 software ver- • A fault routine is one that executes if the controller
sion as many as 100 programs could be scheduled within finds a program fault. Each program can have one
each task. fault routine, if desired.

Routines Tags

Routines are the third level of scheduling within a proj- Unlike conventional controllers, ControlLogix uses a tag-
ect and provide the executable code for the project. Each based addressing structure. Tags are meaningful names,
routine contains a set of logic elements for a specific descriptive of your application and not merely generic

Figure 15-9 Each routine contains a set of logic elements for a specific programming language.
Source: Image Courtesy of Rockwell Automation, Inc.

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