Omron CJ - PROGRAMMING MANUAL 08-2008 Programming Manual page 99

Precautions
Main Conditions Turning ON Condition Flags
Note
Error Flag (P_ER)
The ER Flag will turn ON under special conditions, such as when operand
data for an instruction is incorrect. The instruction will not be executed when
the ER Flag turns ON.
When the ER Flag is ON, the status of other Condition Flags, such as the <,
>, OF, and UF Flags, will not change and status of the = and N Flags will vary
from instruction to instruction.
Refer to the descriptions of individual instructions in the CS/CJ-series Pro-
grammable Controllers Instructions Reference Manual (W340) for the condi-
tions that will cause the ER Flag to turn ON. Caution is required because
some instructions will turn OFF the ER Flag regardless of conditions.
Note The PLC Setup Settings for when an instruction error occurs determines
whether operation will stop when the ER Flag turns ON. In the default setting,
operation will continue when the ER Flag turns ON. If Stop Operation is spec-
ified when the ER Flag turns ON and operation stops (treated as a program
error), the program address at the point where operation stopped will be
stored at in A298 to A299. At the same time, A29508 will turn ON.
Equals Flag (P_EQ)
The Equals Flag is a temporary flag for all instructions except when compari-
son results are equal (=). It is set automatically by the system, and it will
change. The Equals Flag can be turned OFF (ON) by an instruction after a
previous instruction has turned it ON (OFF). The Equals Flag will turn ON, for
example, when MOV or another move instruction moves 0000 Hex as source
data and will be OFF at all other times. Even if an instruction turns the Equals
Flag ON, the move instruction will execute immediately and the Equals Flag
will turn ON or OFF depending on whether the source data for the move
instruction is 0000 Hex or not.
Carry Flag (P_CY)
The CY Flag is used in shift instructions, addition and subtraction instructions
with carry input, addition and subtraction instruction borrows and carries, as
well as with Special I/O Unit instructions, PID instructions, and FPD instruc-
tions. Note the following precautions.
1. The CY Flag can remain ON (OFF) because of execution results for a cer-
tain instruction and then be used in other instruction (an addition and sub-
traction instruction with carry or a shift instruction). Be sure to clear the
Carry Flag when necessary.
2. The CY Flag can be turned ON (OFF) by the execution results for a certain
instruction and be turned OFF (ON) by another instruction. Be sure the
proper results are reflected in the Carry Flag when using it.
Less Than and Greater Than Flags (P_LT, P_GT)
The < and > Flags are used in comparison instruction, as well as in the LMT,
BAND, ZONE, PID and other instructions.
The < or > Flag can be turned OFF (ON) by another instruction even if it is
turned ON (OFF) by execution results for a certain instruction.
Negative Flag (P_N)
The N Flag is turned OFF when the leftmost bit of the instruction execution
results word is "1" for certain instructions and it is turned OFF unconditionally
for other instruction.
Section 2-2
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