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4 SEQUENCE PROGRAM CONFIGURATION AND EXECUTION
CONDITIONS
MELSEC-Q
(b)
When an interrupt factor occurs, the interrupt program with the interrupt
pointer number corresponding to that factor is executed.
However, interrupt program execution varies according to the condition at
that time.
1) If two or more interrupts occur at the same time:
The interrupt programs are executed, starting with the one
corresponding to an interrupt pointer number (I
) of the highest
priority. 2
The remaining interrupt programs remain on stand-by until processing
of the higher priority interrupt program is completed.
If the same interrupt factor as that being executed occurs before the
interrupt program is processed, the interrupt factor is stored in the
memory and, after the interrupt program has been processed, the
same interrupt program is executed again.
2) When an instruction is being executed:
The interrupt program may be executed by interrupting the execution
of an instruction in the main routine program. When the same device is
used in both the main routine program and interrupt program, device
data may be separated.
To prevent the separation of the device data, the following measures
must be taken.
(a) Do not specify the device, to which data will be written in the
interrupt program, directly in the main routine program, but use
another device by shifting the data with a transfer instruction, etc.
(b) If inconvenience is caused when the instruction is interrupted in the
main routine program, execute it after disabling the interruption
with the DI instruction.
However, since the interrupt program will not interrupt during access to
the device of each argument of the instruction, data separation will not
occur on an argument basis.
3) Interruption during a network refresh:
If an interrupt factor occurs during a network refresh operation, the
network refresh operation is suspended, and the interrupt program is
executed.
This means that "assurance of blocks in cyclic data at each station"
cannot be secured by using a device designated as a destination of
link refresh operation on the MELSECNET/H Network System. 3
10ms
10ms
10ms
10ms
Interrupt factor
Interrupt program
execution
Network refresh
execution
Network refresh operation is suspended,
and the interrupt program is executed.
Fig.4.4 Interruption during Network Refresh Operation
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