Allen-Bradley 1756-CNB/E, User Manual

Page: 73 / 186

Publication 1756-UM523F-EN-P - December 2006
Configure and Program the Controller 73
Configured Message Instructions, Continued
Configure Tags for an HMI
To monitor tags directly in the secondary controller (not typical),
monitor from no more than 3 devices through a CNB module.
Monitor tags in a secondary controller only via:
•
RSLogix 5000 programming software.
•
Any method that does not try to create OPC optimized packets.
Only a primary controller can create an OPC optimized packet.
If the message
instruction is
targeted to a
redundant controller Then
During the erroring out
of a message All backplane communications cease. This stoppage allows the redundant controller to receive the message
instruction required to perform a switchover or any diagnostics.
Important: If any of your messages are active during a switchover, you can expect one of these things to
happen:
•
Cached and connected messages cause the message instruction to pause for 7.5 seconds because the
initiating controller has not received a response from the targeted controller. For cached messages, the
message instruction tries to execute three more times, each attempt followed by a pause of 7.5 seconds.
If, after 30 seconds pass, the targeted controller does not respond to the initiating controller, then the
switchover errors out with connected time out
Error 1 Extended Error 203 .
An example of a connected message would be CIP data table read-and-write messages after a
connection has been established.
•
Uncached messages error out after 30 seconds if you have just initiated them because the intiating
controller never received a reply to the forward-open request. The error is
Error 1F Extended Error 204 ,
an unconnected time out.
Examples of uncached messages would include CIP generic messages and messages captured during the
connection process.
During qualification Cached messages run with no errors. A connection has been established.
Connected, but uncached, messages or unconnected messages error out with Error 1 Extended Error 301, No
Buffer Memory .