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• Data communications using the COM instruction
(1) 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
(2) 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
• 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 (2) above, and thus to speed up data communications.
• 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 (1).
• 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.
COM instruction
Step 0
COM instruction
COM instruction
END instruction
COM instruction
• If the scan time from the linked station is longer than the sequence program scan time at the host station, designating the
COM instruction at the host station will not increase the speed of data communications.
Sequence program
Link scan
The programs in which the COM instruction cannot be used are shown below:
• Low-speed execution type programs
• Interrupt programs
• Fixed scan execution type programs
Operation error
• There is no operation error in the COM instruction.
7 APPLICATION INSTRUCTIONS
488
7.6 Structure Creation Instructions
0
0
END
END
END
0
0
COM
0
END
0
COM
COM
0
0
END
Link refresh can be performed
once in each of these intervals.
0
COM
END
0 COM
0
0
0
END
END
END
0
END
COM
COM
END
0
END
0
COM COM
0
END
COM
COM
END
END 0 COM
0
0
END
END
0
END
0
COM
COM
END
0
END
0
COM
END
0
0
COM
END
0
COM
END
COM
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