Mitsubishi MELSEC-Q Series User Manual page 79

4 FUNCTIONS
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(3) Precautions on using the standby master function
(a) Only one standby master station exists in a single data link system.
(b) The total number of stations is 64, including the standby master station. The
number of stations that can be occupied by the standby master station is
one or four.
(c) If an error is detected at the master station in the initial status (before
parameter communication starts), switching to the standby master station
will not be executed.
(d) When the master station becomes faulty, the data link control will
automatically be transferred to the standby master station, but the refresh
instruction of the cyclic data will not be issued. Specify the cyclic data
refresh using the sequence program. Once specified, the information prior to
the error detection at the master station will be output to each station.
(e) When the data link is being controlled by the standby master station, the
master station's parameters cannot be updated.
(f) An error (error code: B39A) occurs at the standby master station if there is a
difference between the station number setting of the station number setting
switches of the standby master station and the station number setting of the
network parameter "standby master station number" of the master station.
If an error has occurred, change the parameter setting of the master station
or the station number setting switch setting of the standby master station,
and then reset the PLC CPU of the standby master station.
(g) If the terminal block of the master station is removed and then replaced in its
original position without turning the power off when the master station is
controlling the data link, both the master and standby master stations
operate as master stations. An error occurs since the data link control has
been transferred to the standby master station ("ERR." LED lights up).
(h) When the master station becomes faulty and the data link control is
transferred to the standby master station, the "ERR." LED of the standby
master station flashes. (This is because the station number of the standby
master station will change from the one set with a parameter to "0" and the
standby station becomes nonexistent. Data link itself is performed normally.)
To avoid this situation, set the standby master station to be an error invalid
station.
(i) The number and range of devices that will be saved by the sequence
program among the data sent from (the station operating as) the master
station to (the station operating as) the standby station may differ according
to the system used.
MELSEC-Q
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