Rockwell Automation Logix5000 Controllers Messages Programming Manual - Manual (Page 11)

Controller messages Chapter 1
Description
The controller scans the MSG instruction.
The rung-condition-in for the MSG instruction is true.
The EN bit is set.
The MSG instruction attempts to enter the queue but 16 throttle positions exist. If all 16 are filled and a
17th message is executed, the message is enabled.
The EW bit remains cleared.
&
The controller scans the MSG instruction.
The rung-condition-in for the MSG instruction is false.
The EN bit remains set.
The MSG instruction attempts to pass through the throttle, but no open positions exist yet.
The EW bit remains cleared.
The controller scans the MSG instruction.
The MSG instruction attempts to enter the queue. This time the throttle position is open and the message
can pass to the message queue.
The EW bit is set.
Depending on how you configure a MSG instruction, it may use a connection to
send or receive data.
This type of message And this communication method Uses a connection
CIP data table read or write — Your option (1)
PLC-2, PLC-3, PLC-5, or SLC (all types)
CIP
CIP with Source ID No
DH+ Yes
CIP generic — Your option (2)
Block-transfer read or write — Yes
(1) CIP data table read or write messages can be connected or unconnected. However for most applications, it is recommended you
leave CIP data table read or write messages connected.
(2) CIP generic messages can be connected or unconnected. However for most applications, it is recommended you leave CIP generic
messages unconnected, unless you want to use the Large Connection option.
If a MSG instruction uses a connection, you have the option to leave the
connection open (cache) or close the connection when the message is done
transmitting.
If you Then
Cache the connection The connection stays open after the MSG instruction is done. This
optimizes execution time. Opening a connection each time the
message executes increases execution time.
Do not cache the connection The connection closes after the MSG instruction is done. This frees up
that connection for other uses.
Cache list
Rockwell Automation Publication 1756-PM012F-EN-P - October 2014 11