Mitsubishi Electric MELSEC iQ-R-R00CPU User Manual page 87

Precautions
The precautions for the interrupt program are mentioned below.
■Restrictions on program creation
• The PLS/PLF instruction performs OFF processing in the scan after the instruction execution. The device turned on
remains on until the interrupt program starts again and the instruction is executed.
• The timer (T, ST) and the counter (C) cannot be used for interrupt programs.
■Data inconsistency
When the interrupt during instruction execution is set to "Enable", processing of an instruction may be suspended and the
interrupt program may be executed. Accordingly, if the interrupted program and the interrupt program both use the same
device, data may become inconsistent. Take the following preventive measures.
• Use the DI instruction to disable the interrupt for an instruction that causes inconsistency when interrupted.
• In an interrupt program, before accessing the device shared by overlapping programs, transfer data to another device in
batch to use, and then write back to the shared device in batch.
• When using the bit data, be careful so that the interrupted program and the interrupt program shall not use the same bit
data.
■If the interrupt accuracy does not increase
If the interrupt accuracy does not increase even when the interrupt during instruction execution is set to "Enable", it may
increase by taking the following measures:
• Limit each character string used in a program to 32 characters or less in length.
• Decrease the multiplex interrupts.
• Reduce the number of times to access the Q series module or the number of points.
• Do not access the Q series module from multiple CPU modules when the multiple CPU system is configured.
■Monitoring the interrupt program execution time
The execution time of the interrupt program can be monitored with the interrupt program in which the inter-module
synchronous interrupt (I44) and multiple CPU synchronous interrupt (I45) are used ( Page 128 Error detection setting)
■When the start-up of an interrupt program is delayed
If the execution interval of the interrupt program is short, the start-up of the interrupt program may be delayed when the
instruction with a long processing time is executed, the online ladder block change is performed, or a Q series module is
accessed simultaneously from multiple CPU modules using instructions in the multiple CPU system configuration. Therefore,
when the execution time is monitored for the interrupt program that uses the inter-module synchronous interrupt (I44) and
multiple CPU synchronous interrupt (I45), an error may be detected in the CPU module ( Page 128 Error detection
setting)
■Consideration when using the data logging function
To use occurrence of an interrupt as a data collection condition, specify the fixed scan interval of the interrupt program, taking
into consideration the processing time of the data logging function. ( Page 216 Using together with interrupt programs)
1 RUNNING A PROGRAM
1.7 Interrupt Program
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