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Precautions Section 2-2
2-2 Precautions
2-2-1 Condition Flags
Using Condition Flags Conditions flags are shared by all instructions, and will change during a cycle
depending on results of executing individual instructions. Therefore, be sure
to use Condition Flags on a branched output with the same execution condi-
tion immediately after an instruction to reflect the results of instruction execu-
tion. Never connect a Condition Flag directly to the bus bar because this will
cause it to reflect execution results for other instructions.
Example: Using Instruction A Execution Results
The same execution condition (a) is used for instructions A and B to execute
instruction B based on the execution results of instruction A. In this case,
instruction B will be executed according to the Condition Flag only if instruc-
tion A is executed.
If the Condition Flag is connected directly to the left bus bar, instruction B will
be executed based on the execution results of a previous rung if instruction A
is not executed.
Note When interrupt tasks are being used, an interrupt task will operate when its
start conditions are met, even during execution of a cyclic task. In this case,
the Condition Flags are returned to their original status when processing
switches back from the interrupt task to the cyclic task, even if those flags
were turned ON/OFF in the interrupt task.
Correct Use
Instruction A
Instruction B
Condition Flag
Example: =
Reflects instruction A
execution results.
Instruction B
Instruction A
Incorrect Use
Preceding rung
Condition Flag
Example: =
Reflects the execution results of
the preceding rung if instruction
A is not executed.
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