Mitsubishi Electric MELSEC-Q Series User Manual page 22

(4) Prevention of a system failure
(a) Continuation of communications upon module error
• Since a bus topology is employed, communications among normal modules continue even if a module
goes down due to power-off or other causes.
• The equipped two-piece terminal block is removable, enabling module change during data link.
Note that if a cable is disconnected, data link fails among all stations.
*1 Power off the module to be replaced before removal. Check that settings of the module that replaces the currently
mounted module are the same as those of the mounted module.
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Data link is continued.
(b) Automatic return when a disconnected station recovers
When the station disconnected from a network due to a data link error recovers, it automatically restarts data
link. The time between an error and a return can be shortened.
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The master/local module can prevent a system failure by using the following functions as well. (
to Page 154, Section 8.3)
• Even if a master station fails, cyclic transmission can be continued by having the standby master station served as
a master station.
• When a module is replaced, error detection can be temporarily disabled.
20
Master station
Master station
Recovering
from the error
Master station
Error
Data link is continued.
Error
Returned
*1
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Page 128, Section 8.2