Allen-Bradley ControlNet Compact GuardLogix 1769, Руководство пользователя, Страница: 85 / 100

Messaging Chapter 6
Make sure of the following:
•
•
The ControlNet modules are connected to a ControlNet network.
•
All wiring and cabling are properly connected.
The communication driver is configured for the programming
workstation.
Guidelines for MSG
Instructions
Follow these guidelines as you work with message instructions.
Table 21 - Guidelines for MSG Instructions
Function Guidelines
For each MSG instruction, create a control tag. Each MSG instruction requires its own control tag. This tag contains control elements for
messages, such as DN and EN, error codes, and information to execute the message, such as
destination path and number of words to transfer:
• Data type = MESSAGE
•
Scope = controller
• The tag cannot be part of an array or a user-defined data type
Keep the source or destination data at the controller
scope.
A MSG instruction can access only tags that are in the Controller Tags folder (controller scope).
If your MSG is to a module that uses 16-bit integers,
use a buffer of INTs in the MSG and DINTs
throughout the project.
If your message is to a module that uses 16-bit integers, such as an SLC 500 controller, and it
transfers integers, not REALs, use a buffer of INTs in the message and DINTs throughout the
project.
This increases the efficiency of your project because Logix5000 controllers execute more
efficiently and use less memory when working with 32-bit integers (DINTs).
If you want to enable more than 16 MSGs at one
time, use some type of management strategy.
If you enable more than 16 MSGs at one time, some MSG instructions may experience delays in
entering the queue. To guarantee the execution of each message, you can take these actions:
• Enable each message in sequence.
•
Enable the messages in smaller groups.
• Program a message to communicate with multiple modules.
• Program logic to coordinate the execution of messages.
Cache connected MSGs that execute most
frequently.
Cache the connection for those MSG instructions that execute most frequently, up to the
maximum number permissible for your controller revision.
This optimizes execution time because the controller does not have to open a connection each
time the message executes.
Limit the number of unconnected and uncached
MSGs to fewer than the number of unconnected
buffers.
The controller can have 10...40 unconnected outgoing buffers:
• The default number is 10.
•
If all the unconnected buffers are in use when an instruction leaves the message queue, the
instruction errors and does not transfer the data.
• You can increase the number of unconnected buffers to a maximum of 40.
For more information on programming MSG instructions, see the Logix5000
Controllers General Instructions Reference Manual, publication 1756-RM003 .
The individual system user manuals for Logix5000 controllers also provide MSG
examples unique to specific controller platforms.