Mitsubishi Electric Melsec QJ71LP21 Reference Manual page 276

7 APPLICATION FUNCTIONS
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POINT
When the SEND instruction is executed to the redundant system, the processing of
the RECV instruction and interrupt program (RECVS instruction) depends on the
following conditions:
(1) When the SEND instruction is executed to the control system and the system
is switched before execution of the RECV instruction and the interrupt
program
If the control system is switched to the standby system before execution of
the RECV instruction and the interrupt program, the control system retains the
instruction execution request flags (SB00A0 to SB00A7) for the RECV
instruction and the interrupt factor (interrupt pointer) of the interrupt program.
If the standby system is returned to the control system due to system
switching, the RECV instruction and the interrupt program will be executed
according to the retained instruction execution request flags and interrupt
factor.
(2) When the SEND instruction is executed to the standby system
When standby system receives data from the sending station, it retains the
instruction execution request flags (SB00A0 to SB00A7) for the RECV
instruction and the interrupt factor (interrupt pointer) of the interrupt program.
If the standby system is switched to the control system, the RECV instruction
and the interrupt program will be executed according to the retained
instruction execution request flags and interrupt factor.
MELSEC-Q
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