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MELSEC-Q
7 APPLICATION FUNCTIONS
The master module issues a system switching request when the status of data link is
changed from "under data link" to "data link halted" (when the D.LINK LED of the
master module turns off).
Although the time interval from when the data link is stopped to when the system
switching request is issued to the control system CPU is set to two seconds, the
interval can be changed using the link special relay (SB) and link special register (SW).
Link special relay and link special register used for setting a system switching monitoring time
Number Name Description
SB0018 Switching monitoring time setting
enable flag
Indicates whether the switching monitoring time setting is enabled or
disabled.
OFF : The switching monitoring time setting (SW0018) is disabled.
ON : The switching monitoring time setting (SW0018) is enabled.
SW0018 Switching monitoring time setting Set a time from the detection of a data link halt to issue of system
switching request in the redundant system.
0: 2s (default)
1 to 500: in 10ms (set up in 10ms units within the range of 10ms to 5s.)
To reduce the system switching time from 2s to 0.5s, set SB0018/SW0018 in the
sequence program as follows.
System switching monitoring
time setting disable directive
System switching monitoring
time setting enable directive
Set up a system switching time of 0.5s.
Enable the SW0018 setting.
Disable the SW0018 setting.
1
1: If SB0018 is disabled (OFF), the system switching monitoring time is 2s (default).
POINT
The master module issues the system switching request to the control system CPU
even when the data link error is caused by the following accident: the master
module mounted in the control system is not connected with a cable or
disconnected at the time of power ON.
The master module issues the system switching request within 4s after power ON.