3.1 Basic Functionality
Programs
3-3
The following table lists the priority, execution conditions, and maximum number of drawings for each
type of ladder drawing.
* Drawings with lower numbers have higher priority.
• Hierarchical Configuration
There are four types of ladder drawings: parent drawings, child drawings, grandchild drawings, and
operation error drawings.
• Parent Drawings
These drawings are automatically executed by the system program when the execution conditions are
met.
• Child Drawings
These drawings are executed when they are called from a parent drawing with a SEE instruction.
• Grandchild Drawings
These drawings are executed when they are called from a child drawing with a SEE instruction.
• Operation Error Drawings
These drawings are automatically executed by the system program when an operation error occurs.
A parent drawing cannot call a child drawing from a different type of drawing. Similarly, a child draw-
ing cannot call a grandchild drawing from a different type of drawing. A parent drawing cannot call a
grandchild drawing directly. The parent drawing first must call the child drawing, and then the child
drawing must call the grandchild drawing. This is called the hierarchical configuration of drawings.
The following figure shows the parent-child-grandchild structure in which a program is created.
Drawing Type Priority* Execution Condition
Maximum
Number of
Drawings
DWG.A (Startup Drawings) 1
Power ON (These drawings are executed once when
the power supply is turned ON.)
64
DWG.I (Interrupt Drawings) 2
External interrupt (These drawings are executed
when a DI interrupt or counter match interrupt is
received from an Option Module.)
64
DWG.H (High-speed Scan
Process Drawings)
3
Started at fixed intervals. (These drawings are exe-
cuted once every high-speed scan.)
200
DWG.L (Low-speed Scan
Process Drawings)
4
Started at fixed intervals. (These drawings are exe-
cuted once every low-speed scan.)
1000
User Functions
Grandchild
Drawings
Child
Drawings
Parent
Drawing
Note: = A, I, H, or L
DWG. DWG.01
DWG.nn
DWG.01.01
DWG.01.02
FUNC-001
FUNC-006
FUNC-032
FUNC-064
DWG.01.03
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