54
Programming Restrictions
Section 2-4
2-4-3 Programming Restrictions
Restrictions in Locating Function Block Instances
No Branches to the Left of
the Instance
Branches are not allowed on the left side of the instance. Branches are
allowed on the right side.
Only One Instance per
Rung
A program rung cannot have more than one instance.
No Function Block
Connections
A function block’s input cannot be connected to another function block’s out-
put. In this case, a variable must be registered to transfer the execution status
from the first function block’s output to the second function blocks input.
Downloading in Task
Units
Tasks including function blocks cannot be downloaded in task units, but
uploading is possible.
Programming
Console Displays
When a user program created with the CX-Programmer is downloaded to the
CPU Unit and read by a Programming Console, the instances will all be dis-
played as question marks. (The instance names will not be displayed.)
Online Editing
Restrictions
The following online editing operations cannot be performed on the user pro-
gram in the CPU Unit.
• Changing or deleting function block definitions (variable table or algo-
rithm)
• Inserting instances or changing instance names
Note The instance’s I/O parameters can be changed, instances can be
deleted, and instructions outside of an instance can be changed.
FB FB
Incorrect Correct
Instruction
Instruction
FB
FB
FB
Incorrect Correct
FB1
EN
XOUT
FB2
XIN1
XIN2
D100
0.0
FB1
EN
XOUT
FB2
EN
XIN1
XIN2
D100
0.0
D3000
D3000
0.0
Temporary variables
transfer the value from
FB1 to FB2.
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