Publication 1756-UM514B-EN-P - February 2003
C-2 Application Guidelines and Tips
Cached Connections
A cached connection is connection between two points that remains
open all the time. Remember the following:
· When using cached connections, more than 1 message from
identical points consume only 1 connection. In this case, ALL the
identical point messages must be cached.
· Messages are completed much faster because the connection is
already open.
· Can have up to 16 cached connections on remote I/O.
· With RSLogix 5000 version 10 and greater, you can have up to
16 connections cached on DH+.
· If more than 16 connections are cached the messages perform
like they were uncached. If you want all connections in your
application to perform like cached connections, we recommend
you only cache 16 connections.
Uncached Connections
An uncached connection is a connection between two points that
opens only when a message is enabled and closes when the
connection is completed. Uncached connections are not as fast as
cached connections.
ControlLogix Controller
Constraints
When using the ControlLogix controllers, you should remember the
following constraints:
· The controller is limited by its unconnected buffers, including a
default Unconnected Buffer (UCB) limit of 10.
· In RSLogix 5000 version 8 and greater, you can increase the UCB
limit to 40. However, for each UCB over 10, your application
receives a penalty of 1K of I/O memory. For example, if you
change the UCB limit to 25, your application loses 15K of I/O
memory.
For more information on Increasing the Unconnected Message
Buffer Limit, see page C-4.
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