Mitsubishi Electric Melsec QJ71LP21 Reference Manual page 351

7 APPLICATION FUNCTIONS
[When the regular network is normal]
Checking cyclic transmission status when regular network is normal
Checking cyclic transmission status when standby network is normal
Switching to regular network when standby network is faulty
(Use of regular network is forced for the 1st scan after RUN.)
Switching to standby network when regular network is faulty
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(3) Program for the simple dual-structured system
The following explains the program that performs refresh switching between the
regular and standby networks.
CPU Regular Standby
SM257:OFF
SM256:OFF
SM262:OFF
SM261:ON
(a) The following shows the program that switches to refresh the standby side
when a faulty station is detected in the regular network. It is necessary to
write the same program to all of the stations in the network.
(b) The following table lists the refresh setting devices (SM) for each network.
Regular/standby network setting status
(Off: Regular On: Standby)
Refreshing from the network modules to
the CPU
(Off: Refreshes On: Does not refresh)
Refreshing from the CPU to the network
modules
(Off: Refreshes On: Does not refresh)
[When there is a faulty area in the regular network]
CPU Regular
SM257:OFF
SM256:ON
CPU Refresh setting of the regular
network module (Refreshes)
CPU Refresh setting of the standby
network module (Does not refresh)
CPU Refresh setting of the regular
network module (Does not refresh)
CPU Refresh setting of the standby
network module (Refreshes)
Module 1 Module 2
SM255 SM260
SM256 SM261
SM257 SM262
MELSEC-Q
Standby
SM262:OFF
SM261:OFF
Module 3 Module 4
SM265 SM270
SM266 SM271
SM267 SM272
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