5
REDUNDANT SYSTEM FUNCTIONS
5.1 Basic Concept of Redundant System
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(5) Operation Mode
The redundant system operates in the following three modes.
(a) Backup mode
The backup mode is for normal operation of redundant system. If a fault or failure
occurs in the control system, the standby system takes over the control and
continues the system control.
(b) Separate mode
The separate mode is for maintenance without stopping control. In the separate
mode, different programs can be run in the control system and standby system
CPU modules. While continuing the system control in the control system, program
of standby system can be corrected and operation of program can be checked by
using the data tracked from the control system. However, in the separate mode,
system switching is not executed even if a fault or failure occurs in the control
system. (System switching can be manually carried out.)
(c) Debug mode
The debug mode is for debugging with a system configuration of only either
system prior to the system operation. In a redundant system, two Redundant
CPUs are normally required; however, debugging can be executed with only one
CPU.
In the debug mode, the CPU module uses the parameters for system A to
operate. Therefore, the station set as system B in the network parameters
becomes absent station (disconnected station).
Check the system switching operation in the backup mode prior to the system
operation because the system switching cannot be checked in the debug mode.
On the programming at system switching, refer to CHAPTER 7 “PROGRAMMING
CAUTIONS”.