Mitsubishi Electric Melsec QJ71LP21 Reference Manual page 371

7 APPLICATION FUNCTIONS
[When station No. 1 is cut off due to a communication error (system switching occurs)]
If a communication error occurs in station No. 1 and it is consequently cut off from the network, the network module automatically
issues a system switching request to the control system CPU, and system switching occurs in the redundant system.
After system switching, station No. 2, a new control system, continues a data link.
Cyclic transmission after system switching in the redundant system is shown below.
Station No. 1
(standby system)
Host station
0000
H
send range
00FF
H
0100 Station No. 3
H
Received data
01FF
H
0200 Station No. 4
H
Received data
02FF
H
1) Station No. 2 takes over the host station send range data handled by station No. 1 (data tracked)
and sends them to other stations without discontinuing a data link.
2) Station No. 2 receives data from other stations.
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(b) Cyclic transmission
Redundant system
Station No. 2
(control system)
Host station
send range
1)
1)
Station No. 3
Received data
Station No. 4
Received data
Station No. 3 Station No. 4
Station No. 1 (2) Station No. 1 (2)
Received data Received data
Received data
Host station
Station No. 3
send range
2)
Station No. 4
Host station
Received data
send range
MELSEC-Q
2)
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