Issue
There are some scenarios where making online modifications on the standby CPU of a hot standby system may be necessary. For example, if there are changes to the process or system configuration that need to be implemented immediately, and the primary CPU is not available, making online modifications on the standby CPU may be necessary to ensure continuity of the process.
Resolution
To make online modifications to an application program, a logic mismatch signal will be enabled to allow a Hot Standby system to continue operating even if there is a mismatch between the applications in the Primary and Standby CPUs. The Logic Mismatch feature will be used to modify an application program and the I/O configuration while the process remains redundant.
This document describes the procedure to perform an online modification to a Modicon M580 Standby controller.
Disclaimer
The views and opinions expressed in this article are those of the author(s) and do not necessarily reflect the official policy or position of Schneider Electric.
