Rockwell Automation Logix5000 Controllers Messages Programming Manual - Manual (Page 19)

Chapter 2
Manage multiple messages
You can use ladder logic to send groups of message (MSG) instructions in
sequence.
• To be processed, each MSG instruction must enter the message queue.
• The queue holds 48 MSGs.
• If more than 16 MSGs are enabled at one time, the message throttle
prevents some of the messages from entering the message queue. If this
occurs, the MSG is held until room exists on the queue for the controller to
process the MSG. On each subsequent scan of the MSG, it checks the queue
to see if room exists.
The message manager logic lets you control the number of MSGs that are enabled
at one time and enable subsequent MSGs in sequence. In this way, MSGs enter
and exit the queue in order and do not need to wait for room on the queue to
become available.
The message manager logic sends three groups of MSGs. Use as many groups as
needed to include all your MSGs.
The Msg_Group tag controls the enabling of each MSG.
• The tag uses the DINT data type.
• Each bit of the tag corresponds to a group of MSGs. For example,
Msg_Group.0 enables and disables the first group of MSGs (group 0).
Example: Message manner logic
To make the example easier to follow, each group contains only two MSGs. In your project, use more MSGs in
each group, such as five.
Initialize the logic
If S:FS = 1 (first scan)
then initialize the MSGs:
Msg_Group = 0, which disables all MSGs.
Msg_Group.0 =1, which enables the first group of MSGs.
Introduction
Message manager logic
Rockwell Automation Publication 1756-PM012F-EN-P - October 2014 19