Omron CJ1G-CPU series, Programming Manual

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54
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.
Rewrite the rungs on the left. They cannot be executed.
The arrows show signal (power flow) flow when the rung consists of control relays.
A
C
B
D
R1
R2
E
A
C
B
D
E
A
C
E
R1
R2
Correct Use
Instruction A
Condition Flag
Example: =
Reflects instruction A
execution results.
Instruction B
LD a
Instruction A
AND =
Instruction B
Instruction Operand
Mnemonic
Incorrect Use
Preceding r ung
Condition Flag
Example: =
Reflects the execution results of
the preceding rung if instruction
A is not e xecuted.
Instruction B
Instruction A