Mitsubishi Electric MELSEC-Q Series User Manual page 185

10 DEVICES
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(4) Precautions
(a) One interrupt pointer is insufficient to execute interrupt counter and interrupt
program operation.
Moreover, an interrupt program cannot be executed by an interrupt counter
setting designated in the PLC system settings in the PLC parameter setting.
(b) If the processing items shown below are in progress when an interruption
occurs, the counting operation will be delayed until processing of these
items is completed.
The count processing starts after the execution of program is completed.
Even if the same interruption occurs again while processing of these items
is in process, only one interruption will be counted.
• During execution of sequence program instructions
• During interrupt program execution
• During execution of a fixed scan execution type program
(c) The maximum counting speed of the interrupt timer is determined by the
longest processing time of the items shown below.
• Instruction with the longest processing time among the instructions used
in the program
• Interrupt program processing time
• The processing time of a fixed scan execution type program
(d) The use of too many interrupt counters will increase the sequence program
processing time, and may cause a "WDT ERROR".
If this occurs, either reduce the number of interrupt counters, or reduce the
counting speed for the input pulse signal.
(e) The interrupt counter's count value can be reset by using the RST C
instruction in the sequence program prior to the FEND instruction.
(f) The interrupt counter's count value can be read out by using the sequence
program MOV instruction.
MELSEC-Q
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