Mitsubishi MELSEC Q Series, Programming Manual

Page: 452 / 816

7-112
7.6 Structured Instructions
7.6.5 Refresh instruction
COM
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.
(6) If the scan time from the linked station is longer than the sequence program scan time at the
host station, specifying the COM instruction at the host station will not increase the speed of
data communications.
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
O peration Error
No operation error occurs in the execution of the COM instruction.
S tep 0
COM i nstruct i on
COM i nstruct i on
COM i nstruct i on
EN D
COM i nstruct i on
Li n k refresh can b e performe d
once i n each of these i nterva l s .
S equence program
0
END
COM
Lin k scan
0 COM
END
0 COM COM 0
END
END