Modicon M580 Hot Standby Frequently Used Architectures, System Guide

The M580 Hot Standby system is designed for use where downtime cannot be tolerated. The system delivers high availability through redundancy. Two backplanes are configured with identical hardware and software. One of the controllers acts as the primary, which runs the application by executing program logic and operating RIO drops and distributed equipment. The other controller acts as the standby controller. The primary controller updates the standby controller at the beginning of each scan. The standby is ready to assume control within one scan if the primary stops communications. Primary and standby states are interchangeable. When the controllers are running, either controller can enter the primary state. When one running controller becomes primary, the other running controller may be in the standby or wait state. The EIO and DIO networks are operated by the primary controller.