Msg Instruction Ladder Logic - Allen-Bradley MicroLogix 1400 Instruction Manual

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MSG Instruction Ladder
Logic
When the Communications Servicing Selection bit is unchecked, at the
next execution of a Service Communications (SVC) instruction, I/O
Refresh (REF) instruction, or when it performs Communications Servicing,
whichever occurs first, commands/replies are processed as follows:
• One incoming channel 0 or channel 1 command;
• (conditional) If the Message Servicing Selection is clear (not
checked) first, all incoming channel 0 or channel 1 message replies;
then all outgoing channel 0 or channel 1 messages on the overflow
queue. If the Message Servicing Selection is set (checked), First the
incoming channel 0 or channel 1 message reply; then one outgoing
channel 0 or channel 1 message on the overflow queue.
• All remaining incoming channel 0 or channel 1 commands.
Message Servicing Selection
Use this check box to enhance communication capability. If this is
checked and the Communication Servicing Selection check box is not
checked the MSG functionality throughput (and scan time) will increase.
• When this check box is checked, the controller services one
outgoing channel 0 or channel 1 MSG instruction at the next Service
Communications (SVC) instruction, I/O Refresh (REF) instruction, or
when it performs Communications Servicing. When this check box
is clear (unchecked), the controller services all outgoing channel 0
or channel 1 MSG instructions at the next Service Communications
(SVC) instruction, I/O Refresh (REF) instruction, or when it performs
Communications Servicing.
• The Message Servicing Selection (Channel 0 or channel 1) bit is
applied by the controller when the Communications Servicing
Selection (Channel 0 or channel 1) bit is clear (unchecked).
Enabling the MSG Instruction for Continuous Operation
The message instruction is enabled during the initial processor program
scan and each time the message completes. For example, when the DN or
ER bit is set.
Communications Instructions
Publication 1766-RM001A-EN-P - October 2008
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