408
COM
Function
(1) Use the COM instruction for the following purposes.
(a) To reduce the time required to send/receive data to/from the remote I/O stations.
(b) To ensure data communication with a CPU module on another station when two CPU modules perform operations
using different scan times.
(2) The processing of the COM instruction differs depending on the status (ON or OFF) of the special relay SM775.
• SM775 is OFF: Performs both auto refresh and communication with external devices. *
1
*
2
• SM775 is ON: Performs only communication with external devices.*
1
*1: The following processing is performed in communication with external devices.
• Monitor processing of other stations
• Read processing by the serial communications module of the buffer memory of another intelligent function module
*2: The auto refresh includes the following processing:
• Refresh of MELSECNET/10H
• CC-Link refresh
• Auto refresh of intelligent function modules
(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. Note, however, that the scan time of the
sequence program will increase by the time taken for communication with external devices and auto refresh (including
link refresh) of 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.
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
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