Allen-Bradley 1756-CNB/E, User Manual

Page: 72 / 186

Publication 1756-UM523F-EN-P - December 2006
72 Configure and Program the Controller
Configure Message (MSG) Instructions
Configured Message Instructions
If the MSG instruction
is Then
From a redundant
controller In a redundant controller, any MSG instruction that is in progress during a switchover experiences an error.
(The ER bit of the instruction turns on.) After the switchover, normal communication resumes.
To a redundant controller For any MSG instruction from a controller in another chassis to a redundant controller, cache the connection:
42977
Leave this box checked.
Path to the
Redundant
Controller.
Properties of the Message to the Redundant Controller
If the MSG instruction
originates from a
redundant controller Then
During a switchover The message instructions status bits are updated asynchronously to the program scan. Consequently, you
cannot crossload your message instructions status bits to a secondary controller.
During a switchover, any active message instructions become inactive. When this occurs, you will need to
reinitialize the execution of your message instructions in the new primary controller.
During qualification The scrolling display changes from CMPT for compatible to Qfng for qualifying.
•
If a configured message is cached, the primary controller automatically establishes a connection with no
errors.
•
If a configured message is uncached or unconnected, the primary controller receives Error 1 Extended
Error 301, No Buffer Memory .