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Checking Programs Section 1-3
The ER Flag (error Flag) will turn OFF if the instruction (excluding input
instructions) ends normally. Conditions that turn ON the ER Flag will vary with
individual instructions. See descriptions of individual instructions in for details.
If Instruction Errors are set to Stop Operation in the PLC Setup, then opera-
tion will stop (fatal error) and the Instruction Processing Error Flag (A295.08)
will turn ON if an instruction processing error occurs and the ER Flag turns
ON.
Illegal Access Errors Illegal access errors indicate that the wrong area was accessed in one of the
following ways when the address specifying the instruction operand was
accessed.
1,2,3... 1. A read or write was executed for a parameter area.
2. A write was executed in a memory area that is not mounted (See note.).
3. A write was executed in a read-only area.
4. The value specified in an indirect DM address in BCD mode was not BCD
(e.g., *D1 contains #A000).
Note An IR register containing the internal memory address of a bit is
used as a word address or an IR containing the internal memory
address of a word is used as a bit address.
Instruction processing will continue and the Error Flag (ER Flag) will not turn
ON if an access error occurs, but the Access Error Flag (AER Flag) will turn
ON.
If Instruction Errors are set to Stop Operation in the PLC Setup, then opera-
tion will stop (fatal error) and the “Illegal Access Error Flag” (A295.10) will turn
ON if an illegal access error occurs and the AER Flag turns ON.
Note The Access Error Flag (AER Flag) will not be cleared after a task is executed.
If Instruction Errors are set to Continue Operation, this Flag can be monitored
until just before the END(001) instruction to see if an illegal access error has
occurred in the task program. (The status of the final AER Flag after the entire
user program has been executed will be monitored if the AER Flag is moni-
tored on the CX-Programmer.)
Other Errors
Illegal Instruction Errors Illegal instruction errors indicate that an attempt was made to execute instruc-
tion data other than that defined in the system. This error will normally not
occur as long as the program is created on a the CX-Programmer.
In the rare even that this error does occur, it will be treated as a program error,
operation will stop (fatal error), and the Illegal Instruction Flag (A295.14) will
turn ON.
UM (User Memory)
Overflow Errors
UM overflow errors indicate that an attempt was made to execute instruction
data stored beyond the last address in the user memory (UM) defined as pro-
gram storage area. This error will normally not occur as long as the program is
created on the CX-Programmer.
In the rare even that this error does occur, it will be treated as a program error,
operation will stop (fatal error), and the UM Overflow Flag (A295.15) will turn
ON.
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