Mitsubishi Electric Q81BD-J61BT11 User Manual page 84

4 FUNCTIONS
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(3) Notes on using the standby master function
(a) Only one standby master station is allowed in a single data link system.
(b) The total number of stations can be no more than 64, including the standby
master station. The number of stations that can be occupied by the standby
master station is one or four.
(c) Do not specify station number 64 for a system in which a standby master
station exists.
If it is specified, station number 64 cannot communicate normally.
(d) If any abnormality is detected at the master station in the initial status (before
parameter communication starts), the switch to the standby master station
will not be executed.
(e) When the master station becomes faulty, the data link control will
automatically be transferred to the standby master station, but the cyclic
transmission data will not be transferred. Instructs to perform the switching
direction (SB0001 is ON) with a user program.
After switching the data link startup (SB0043) from the standby master
station to the master station is completed, the information before the
detection of abnormality at the master station will be output to each station.
Note that, a transient transmission to the master station cannot be
performed until switching the data link startup (SB0043) from the standby
master station to the master station is completed.
(If the transient transmission is performed before the switching is completed,
a timeout error will occur in the request source.)
Perform transient transmission to the master station after instructing to
perform the switching direction of the cyclic transmission data with a user
program.
(f) The master station duplex function is not available.
The control is switched from the standby master station to the master station
only once.
Therefore, if the standby master station goes down after the control has
been switched to the standby master station due to master station failure,
the CC-Link system will stop the data link. (The control will not be switched
even if the master station functions properly.)
(g) When the master station goes down and the data link control right is
switched to the standby master station, the standby master station number is
identified an error number (Corresponding bits in SB0080 or SW0080 to
SW0083 turn ON.) The station number of the standby master station is
changed to 0 from the station number set by the parameter because there is
no standby master station. The data linking is successfully performed.
Specifying a standby master station as an error invalid station prevents this
kind of error detection.
(h) When the standby master station is controlling the data link, parameters
cannot be updated.
MELSEC
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