Mitsubishi Electric melsec q00ujcpu User Manual page 51

(4) Processing at program execution type change
When the program execution type is changed from the scan execution type to the interrupt, the CPU
module saves and restores the following data. (
• Data in the index register
• File register block number
Whether to save and restore the data above can be set in the PLC parameter dialog box.
If the data is not saved or restored, the overhead time of the corresponding interrupt program can be shortened.
( Section 10.1.2)
(5) Restrictions
(a) When the same device is used
During execution of an instruction in a main routine program, an interrupt program may be
executed, suspending the processing of the instruction being executed.
If the same device is used for the main routine program and interrupt program, device data may
become inconsistent. In this case, take the following measures to prevent device data
inconsistency.
1) Moving device data to another device
Do not directly specify the device where the data is written by the interrupt program in the main
routine program. Use the data in another device by moving the data with the transfer instruction.
2) Disabling interrupts with the DI instruction
Disable interrupts with the DI instruction if instructions that may cause inconvenience for the main
routine program are used.
However, interrupts do not occur during access to the device of the corresponding argument of the
instruction. For this reason, data inconsistency will not occur in units of arguments.
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Section 9.6.3)