MSG Instruction Behavior During Qualification and Switchover
During qualification of the redundant chassis pair, MSG instructions operate as follows:
- The status message on the front of the redundancy module displays QFNG for qualifying.
- If a configured message is cached, the primary controller automatically establishes a connection with the secondary controller with no errors.
- If a configured message is uncached or unconnected, the message experiences the following error: Error 1 Extended Error 301, No Buffer Memory.
During a switchover, MSG instructions operate as follows:
- In the primary controller, the message instruction status bits update asynchronously to the program scan. Consequently, you cannot crossload your message instructions status bits to a secondary controller.
- Any active message instructions in the old primary controller become inactive. When the switchover occurs, you must reinitialize the execution of your message instructions in the new primary controller.
- Cached and connected messages cause the message instruction to pause for 7.5 seconds because the primary controller has not received a response from the secondary controller:
- For cached messages, the message instruction tries to execute three more times, each attempt followed by a pause of 7.5 seconds. If 30 seconds pass and the targeted controller does not respond to the initiating controller, then the switchover errors out with connected timeout Error 1 Extended Error 203. An example of a connected message is CIP™ data table read-and-write messages after a connection has been established.
- Uncached messages error out after 30 seconds if you have initiated them because the initiating controller never received a reply to the forward-open request. The error is Error 1F Extended Error 204, an unconnected timeout. Examples of uncached messages include CIP generic messages and messages that are captured during the connection process.
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