Condition Flags - Omron CJ - 09-2009 Operation Manual

Condition Flags

9-20 Condition Flags

Summary of the Condition
Flags
Name
Error Flag P_ER
Access Error Flag P_AER
Carry Flag P_CY
Greater Than Flag P_GT
Equals Flag P_EQ
Less Than Flag P_LT
Negative Flag P_N
Overflow Flag P_OF
Underflow Flag P_UF
Greater Than or P_GE
Equals Flag
Not Equal Flag P_NE
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These flags include the Arithmetic Flags such as the Error Flag and Equals
Flag which indicate the results of instruction execution. In earlier PLCs, these
flags were in the SR Area.
The Condition Flags are specified with labels, such as CY and ER, or with
symbols, such as P_Carry and P_Instr_Error, rather than addresses. The sta-
tus of these flags reflects the results of instruction execution, but the flags are
read-only; they cannot be written directly from instructions or Programming
Devices (CX-Programmer or Programming Console).
Note The CX-Programmer treats condition flags as global symbols beginning with
P_.
All Condition Flags are cleared when the program switches tasks, so the sta-
tus of the ER and AER flags are maintained only in the task in which the error
occurred.
The Condition Flags cannot be force-set and force-reset.
The following table summarizes the functions of the Condition Flags, although
the functions of these flags will vary slightly from instruction to instruction.
Refer to the description of the instruction for complete details on the operation
of the Condition Flags for a particular instruction.
Symbol Label
ER Turned ON when the operand data in an instruction is incorrect (an
instruction processing error) to indicate that an instruction ended
because of an error.
When the PLC Setup is set to stop operation for an instruction error
(Instruction Error Operation), program execution will be stopped and
the Instruction Processing Error Flag (A29508) will be turned ON
when the Error Flag is turned ON.
AER Turned ON when an Illegal Access Error occurs. The Illegal Access
Error indicates that an instruction attempted to access an area of
memory that should not be accessed.
When the PLC Setup is set to stop operation for an instruction error
(Instruction Error Operation), program execution will be stopped and
the Instruction Processing Error Flag (A429510) will be turned ON
when the Access Error Flag is turned ON.
CY Turned ON when there is a carry in the result of an arithmetic opera-
tion or a "1" is shifted to the Carry Flag by a Data Shift instruction.
The Carry Flag is part of the result of some Data Shift and Symbol
Math instructions.
> Turned ON when the first operand of a Comparison Instruction is
greater than the second or a value exceeds a specified range.
= Turned ON when the two operands of a Comparison Instruction are
equal the result of a calculation is 0.
< Turned ON when the first operand of a Comparison Instruction is less
than the second or a value is below a specified range.
N Turned ON when the most significant bit (sign bit) of a result is ON.
OF Turned ON when the result of calculation overflows the capacity of the
result word(s).
UF Turned ON when the result of calculation underflows the capacity of
the result word(s).
>=
Turned ON when the first operand of a Comparison Instruction is
greater than or equal to the second.
< > Turned ON when the two operands of a Comparison Instruction are
not equal.
Section 9-20
Function