Save the ON/OFF status of SM1636 (Previous control system identification flag) to 'System B restart flag' since SM1636 is on during only one scan after

the operating status of the CPU module has changed to RUN.

(3)

Execute the subroutine program (P100) while 'System B restart flag' is on.

Jump to the END instruction not to execute the user program while 'System B restart flag' is on.

(41) Terminate the main routine program.

(57) Start measuring the timeout time (ten seconds (Timer limit setting: 100ms)) for the startup of previous control system.

Execute the SP.CONTSW instruction when the data link status of the network modules in the system B is normal and no system switching requests are

received from them. Check the one from SW1B0 to SW1B7 for the data link status of the network modules in the system B. (Device and bit vary

depending on the network modules and the station number in the system B.) Check SD1646 (System switching request status from a network module of

the other system) whether system switching requests are received from the network modules in the system B.

Enable the manual system switching after the network module communications in the system B have been established successfully.

Execute the system switching instruction.

Turn off 'System B restart flag'.

Turn off 'System B restart flag' as well when the timeout time (ten seconds) has elapsed, because system switching is not performed and the CPU module

proceeds to the next scan to execute the user program while the system A remains as the control system. (The timeout time (ten seconds) needs to be

adjusted depending on the system configuration and environment.)

(77) Terminate the subroutine program.

11 BASIC CONCEPT OF REDUNDANT SYSTEM

172

11.6 System Determination

User program

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