Mitsubishi Electric MELSEC Q Series Reference Manual page 145

(5) Cyclic transmission processing when system switching is requested to the
control system CPU
The following are examples of link relay (LB) data transmission.
Ex.
(a) When both systems are powered ON
When a redundant system is normal, the system A acts as the control system and starts data link.
System A
(control system)
Control station
No.1
LB0 to LBFF
LB100 to LB1FF
LB200 to LB2FF
LB7FFF
(b) When a system switching occurs due to a communication error on the control
system
If station No.1 is disconnected from the network due to a communication error, a system switching request is
issued to the control system CPU, resulting in system switching.
The new control system (station No.2) continues data link.
Cyclic transmission after the system switching is illustrated below.
System A
(standby system)
Disconnected
station No.1
Communication
error
LB0 to LBFF
LB100 to LB1FF
LB200 to LB2FF
LB7FFF
Redundant system
System B
(standby system)
Normal station
No.2
Tracking cable
Link relay (LB)
No.1, 2 send range
No.3 No.3
No.4 No.4
The same send range is used for station
No.1 and 2 by tracking transfer.
Redundant system
System B
(control station)
Sub-control station
No.2
System switched
Tracking cable
Link relay (LB)
No.1, 2 send range No.1, 2 send range
No.3 No.3
No.4 No.4
Data in No.1, 2 send range are sent
from station No.2.
Normal station Normal station
No.3 No.4
No.1, 2 No.1, 2
No.3 send range No.3
No.4 send range
No.4
Normal station Normal station
No.3 No.4
No.1, 2 No.1, 2
No.3 send range No.3
No.4 send range
No.4
CHAPTER 4 FUNCTIONS
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