Mitsubishi MELSEC Q Series Programming Manual page 509
Common instruction 1/2
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(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.
Execution of COM instruction
0
(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
Host station program
Data communications
Program at other station
I/O refresh at remote I/O station
(b) Example of data communications when COM instruction has been used
Host station program
Data communications
Program at other station
I/O refresh at remote I/O station
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.
Step 0
COM instruction
COM instruction
Execution of COM instruction
END
0
END
General data processing and auto refresh
(including link refresh) of intelligent function module
0
0
END
0
END
END
0
END
0
END
COM
COM
0
END
0
END
0
COM COM
COM
COM
0
0
END
COM instruction
Link refresh can be performed
COM instruction
once in each of these intervals.
END instruction
0
0
END
0
END
0
END
0
END
0
END
COM
COM
COM
END
0
END
0
END
COM
0
END
0
END
COM
COM
COM
COM
1
2
3
4
6
6
0
7
8
0
COM
0
0
END
7-135
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