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Checking Programs Section 1-3
1-3-4 Checking Fatal Errors
The following errors are fatal program errors and the CPU Unit will stop run-
ning if one of these occurs. When operation is stopped by a program error, the
task number where operation stopped will be stored in A294 and the program
address will be stored in A298/A299. The cause of the program error can be
determined from this information.
Note If the Error Flag or Access Error Flag turns ON, it will be treated as a program
error and it can be used to stop the CPU from running. Specify operation for
program errors in the PLC Setup.
Address Description Stored Data
A294 The type of task and the task number at the
point where operation stopped will be stored
here if operation stops due to a program error.
Note FFFF hex will be stored if there are no
active cyclic tasks in a cycle, i.e., if there
are no cyclic tasks to be executed.
Cyclic task: 0000 to 001F hex (cyclic tasks 0 to 31)
Interrupt task: 8000 to 80FF hex (interrupt tasks 0 to 255)
A298/A299 The program address at the point where opera-
tion stopped will be stored here in binary if
operation stops due to a program error.
Note If the END(001) instruction is missing
(A295.11 will be ON), the address where
END(001) was expected will be stored.
Note If there is a task execution error (A295.12
will be ON), FFFFFFFF hex will be stored
in A298/A299.
A298: Rightmost portion of program address
A299: Leftmost portion of program address
Program error Description Related flags
No END Instruction An END instruction is not present in the
program.
The No END Flag (A295.11) turns ON.
Error During Task Execution No task is ready in the cycle.
No program is allocated to a task.
The corresponding interrupt task number is
not present even though the execution
condition for the interrupt task was met.
The Task Error Flag (295.12) turns ON.
Instruction Processing Error (ER
Flag ON) and Stop Operation set
for Instruction Errors in PLC Setup
The wrong data values were provided in
the operand when an attempt was made to
execute an instruction.
The ER Flag turns ON and the Instruc-
tion Processing Error Flag (A295.08)
turns ON if Stop Operation set for
Instruction Errors in PLC Setup.
Illegal Access Error (AER Flag ON)
and Stop Operation set for Instruc-
tion Errors in PLC Setup
A read or write was executed for a parame-
ter area.
A write was executed in a memory area
that is not mounted.
A write was executed in a read-only area.
The value specified in an indirect DM
address in BCD mode was not BCD.
AER Flag turns ON and the Illegal
Access Error Flag (A295.10) turns ON
if Stop Operation set for Instruction
Errors in PLC Setup
Indirect DM BCD Error and Stop
Operation set for Instruction Errors
in PLC Setup
The value specified in an indirect DM
address in BCD mode is not BCD.
AER Flag turns ON and the DM Indi-
rect BCD Error Flag (A295.09) turns
ON if Stop Operation set for Instruction
Errors in PLC Setup
Differentiation Address Overflow
Error
During online editing, more than 131,072
differentiated instructions have been
inserted or deleted.
The Differentiation Overflow Error Flag
(A295.13) turns ON.
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