Mitsubishi Electric MELSEC-Q Series - Page 145

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CHAPTER 4 FUNCTIONS
4
4.7 Redundant-CPU-Compatible Function 4.7.2 System switching request to control system CPU
(5) Cyclic transmission processing when system switching is requested to the
control system CPU
Ex.
The following are examples of link relay (LB) data transmission.
(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.
(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.
Redundant system
Tracking cable
Normal station
No.3
Normal station
No.4
Link relay (LB)
LB0 to LBFF
LB100 to LB1FF
LB200 to LB2FF
LB7FFF
No.1, 2 send range
No.3 No.3
No.4
No.3
No.4 No.4
No.1, 2 No.1, 2
No.3 send range
No.4 send range
The same send range is used for station
No.1 and 2 by tracking transfer.
System A
(control system)
Control station
No.1
System B
(standby system)
Normal station
No.2
LB7FFF
LB0 to LBFF
LB100 to LB1FF
LB200 to LB2FF
Data in No.1, 2 send range are sent
from station No.2.
Communication
error
System switched
Redundant system
Tracking cable
Normal station
No.3
Normal station
No.4
Link relay (LB)
No.1, 2 send range No.1, 2 send range
No.3 No.3
No.4
No.3
No.4 No.4
No.1, 2 No.1, 2
No.3 send range
No.4 send range
System A
(standby system)
Disconnected
station No.1
System B
(control station)
Sub-control station
No.2