Allen-Bradley ControlLogix - Determining Connections for Messaging

1756-6.5.3 - December 1999
A-8 Allocating Communication Connections
Determining Connections
for Messaging
Some types of messages use a connection to send or receive data. Some also
give you the option of either leaving the connection open (cache) or closing
the connection when the message is done transmitting. The following table
shows which messages use a connection and whether or not you can cache
the connection:
Use the following table to select a cache option for a message.
This type of message
Using this
communication method
Uses a
connection
Which you can
cache
CIP data table read or write CIP
á
á
PLC2, PLC3, PLC5, or SLC (all
types)
CIP
CIP with Source ID
DH+
á
CIP generic N/A
block-transfer read or write N/A
áá
If the message
executes Then Because
repeatedly Select the Cache
Connections check box
This will keep the connection open and
optimize execution time. Opening a
connection each time the message
executes increases execution time.
infrequently Clear the Cache
Connections check box
This will close the connection upon
completion, which frees up that
connection for other uses.