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7-135
COM
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7.6 Structure creation instructions
7.6.9 Refresh instruction (COM)
(3) At the point of the execution of the COM instruction, the CPU module temporarily stops the
processing of the sequence program, and performs the same operation as ordinary data
processing as well as auto refresh of intelligent function modules (including link refreshes) at
the END processing. However, the low speed cyclic refresh of
MELSECNET/10 or MELSECNET/H is not performed.
(4) The COM instruction can be used in a sequence program any number of times. However,
note that the scan time of the sequence program will be lengthened by the time taken for
communication with peripheral device and the auto refresh (including the link refresh) of the
intelligent function modules.
(5) Data communications using the COM instruction
(a) Example of data communications when COM instruction is not used
(b) Example of data communications when COM instruction has been used
1) When the COM instruction is used at the host station, it is possible to increase the number
of data communication repetitions with the remote I/O station unconditionally, as shown in
(b) above, and thus to speed up data communications.
2) In cases where the remote station scan time is longer than the scan time of the host
station, the COM instruction used at the remote station side can avoid the occurrence of
timing failure in which the data cannot be fetched, as shown in (a).
3) When the COM instruction has been used at the other station, a link refresh will be
performed each time that station receives a command from the host station.
0
END
0
END
0
Execution of COM instruction Execution of COM instruction
General data processing and auto refresh
(including link refresh) of intelligent function module
Host station program
0
0
END
END
0
END
Data communications
Program at other station
I/O refresh at remote I/O station
END
0
END
0
END
0
END
0
0
0
END
0
END
0
0
END
Host station program
Data communications
Program at other station
0
END
0 0
0
END
COM
COM
0
END
COM
0
END
COM
0
END
COM
0
COM
0 END 0
0
COM
COM COM
COM
COM
COM
COM
END
ENDEND
COM
I/O refresh at remote I/O station
Step 0
COM instruction
COM instruction
COM instruction
END instruction
COM instruction
Link refresh can be performed
once in each of these intervals.