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7.1 Instructions Restricted in Use for Redundant System
7
PROGRAMMING CAUTIONS
(5) Instructions that Change CPU Status
When the instruction listed in Table7.3 is executed and the control system CPU
module status changes, the information of the changed status will not be sent to the
standby system CPU module.
Therefore, if system switching occurs, it is necessary to use the user program to
execute that instruction in the new control system CPU, as necessary.
(6) Restrictions when Using Special Relay (SM1518) "Standby System to
Control System Switching Status Flag"
This section explains how the rise instruction, for which SM1518 has been set as its
execution condition, is processed after system switching, on the assumption that
signal flow memory has not been tracked.
(a) Processing
When system switching occurs, the control system CPU module turns on signal
flow memory in all steps.
Therefore, the rise instruction, for which SM1518 has been set as its execution
condition, cannot be executed after system switching.
Create a program to be executed at the time of SM1518 shutdown using
shutdown pulse operation contact as shown in the diagram below when startup
execution instructions with SM1518 execution conditions are executed.
The instruction is executed at the second scan after system switching, in order
that the fall instruction will be executed upon SM1518 fall.
Table7.3 Instructions that Change CPU Status
Instruction Classification Instruction Symbol
Program Execution Control
Disable Interrupt DI
Enable Interrupt EI
Interrupt Disable/Enable Setting IMASK
Change Instruction
File Register Block No. Change RSET
File Register File Set QDRSET
Comment File Set QCDSET
Application Instruction Timing Clock DUTY
Diagram 7.4 Program for DUTY Instruction Using SM1518
Diagram 7.5 Program That Executes DUTY Instruction on the Falling Edge of SM1518
After system switching, startup execution instructions are not run.
SM1518
0
DUTY K1 K3 SM420
After system switching, perform
DUTY instruction during
SM1518 shutdown.
SM1518
0
DUTY K1 K3 SM420
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