Rockwell Automation Logix5000 Controllers IEC 61131-3 Compliance Programming Manual - Manual (Page 10)

10 Rockwell Automation Publication 1756-PM018C-EN-P - November 2012
Chapter 1 IEC61131-3 Compliance
Operating System The preemptive, multitasking operating system (OS) of Logix5000 controllers
complies with the IEC61131-3 definition. In IEC61131-3, the programmable
controllers OS can contain zero or more tasks, that can execute one or more
programs each containing one or more functions or routines. According to
IEC61131-3, the number of each of these components is implementation
dependent. Logix5000 controllers provide multiple tasks, each containing
multiple programs and an unlimited number of functions or routines.
IEC61131-3 provides an option for creating different task execution
classifications. Tasks may be configured as continuous, periodic, or event based. A
continuous task does not need to be scheduled in that it will utilize any left over
processing time when other tasks are dormant. Periodic tasks are scheduled to
operate based on a reoccurring time period. The IEC61131-3 specification does
not specify a time base for periodic task configuration. An IEC61131-3 event
based task is triggered upon detection of the rising edge of a configured input.
Logix5000 controllers support both continuous and periodic tasks. Additionally,
the period for a periodic task is configurable starting as low as 1 millisecond (ms).
Data Definitions The IEC61131-3 specification provides access to memory through the creation
of named variables. IEC61131-3 names for variables consist of a minimum of six
characters (Logix Designer application supports a minimum of 1 character)
starting with an underscore “_” or an alpha character (A-Z), followed by one or
more characters consisting of an underscore “_”, alpha character (A-Z) or a
number (0-9). Optionally, lower case alpha characters (a-z) can be supported as
long as they are case insensitive (A = a, B = b, C = c …). Logix5000 controllers
provide full compliance with this definition, support the lower case option, and
extend the name to support up to 40 character names.
Data variables in IEC61131-3 may be defined such that they are accessible to all
programs within a resource or controller, or limited access is provided only to the
functions or routines within a single program. To pass data between multiple
resources or controllers, access paths may be configured to define the location of
the data within a system. Logix5000 controllers provide compliance by providing
program scoped, controller scoped data and permits the configuration of access
paths using produced/consumed data.
The memory interpretation of a variable within IEC61131-3 is defined through
the use of either an elementary data type or an optional derived data type that is
created from a group of multiple data types. Logix5000 controllers support the
use of the BOOL (1 bit), SINT (8 bit integer), INT (16 bit integer), DINT (32
bit integer) and REAL (IEEE floating point number) elementary data types.
Additionally, the optional derived data types are supported through the creation
of user defined structures and arrays.