Self-Diagnostic Function - Mitsubishi Electric 700 Series Programming Manual

3.16 Self-diagnostic Function

The self-diagnostic function diagnoses faults by the built-in PLC function itself.
(1) Self-diagnostic timing
The self-diagnostic function is performed at power-on, at reset, at execution of
any instruction, or at execution of the END instruction.
1) At power-on, at reset
Whether operation can be executed or not is diagnosed.
2) At execution of any instruction
An error occurs if the operation of any instruction in the sequence program is
not executed properly.
CAUTION
For the LD, AND, OR, logical comparison operation, and OUT instructions, the set
devices are always checked. For the other instructions (SET, RST, MOV, etc.), a
check is made as soon as the execution condition holds and the instruction is
ready to be executed.
3) At execution of END instruction
Operation clog up monitor timer
(2) Operation mode at fault detection
There are two different PLC operation modes at detection of a fault by the self-
diagnostic: operation stop mode and operation continuation mode.
The operation continuation mode includes a fault that enables operation to be
stopped by built-in PLC function parameter setting. (Refer to page 94)
1) If an operation stop error is detected by the self-diagnostic, operation is
stopped and outputs (Y) are all turned off as soon as the error is detected. The
other devices maintain their states at occurrence of the error.
2) If an operation continuation error is detected, only the faulty program part is not
executed and the program at the next step is executed.
(3) Error definition checking
When M9008 (self-diagnostic error) turns on at detection of an error, the error
code is stored into D9008 (self-diagnostic error). Especially in the continuation
mode, use it in the program to prevent a mechanical system malfunction.
For the errors detected by the self-diagnostic, refer to the error code list on page
172 .
Self-diagnostic Function
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