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4 Understanding Programming
4-2
Tasks, Sections, and Symbols
4-2-1
Overview of Tasks
There are basically two types of tasks.
Task settings must be made to use interrupt tasks with a CP1E CPU Unit.
Task type
Cyclic task
Interrupt tasks
4-2-2
Overview of Sections
With the CX-Programmer, programs can be created and displayed in functional units called sections.
Any program in a task can be divided into sections.
Sections improve program legibility and simplifies editing.
4-2-3
Overview of Symbols
Symbols
I/O memory area addresses or constants can be specified by using character strings registered as symbols.
The symbols are registered in the symbol table of the CX-Programmer.
Programming with symbols enables programming with names without being aware of the addresses.
The symbol table is saved in the CX-Programmer project file (.CXP) along with other parameters, such
as the user programs.
Symbol Types
There are two types of symbols that can be used in programs.
Global Symbols
Global symbols can be accessed from all ladder programs in the PLC.
Local Symbols
Local symbols can be accessed from only one task. They are assigned to individual tasks.
4-6
Description
Executed once per cycle
Executed when a specific
condition occurs. The process
being executed is interrupted.
Applicable
programming
Execution condition
language
Ladder diagram Only one for the CP1E.
(Normally, the user does not have to con-
sider this.)
Ladder diagram An interrupt task is placed into READY
status when the interrupt condition
occurs. A condition can be set for the fol-
lowing interrupt tasks.
• Scheduled interrupt tasks
• I/O interrupt tasks
CP1E CPU Unit Software User's Manual(W480)
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