User manual

Publication CNET-UM001C-EN-P - November 2005
Control I/O 4-5
Direct or Rack Optimized Connection
Logix5000 controllers use connections to transmit I/O data. These
connections can be direct connections or rack optimized connections.
This Term Means
Direct Connection A direct connection is a real-time, data transfer link between the controller and an I/O module–analog or digital.
This connection enables your controller to collect more data from an I/O module. For example, with a direct
connection, the controller can collect diagnostic status data from a 1756-IA8D module that would not be
collected in a rack optimized connection.
The controller maintains and monitors the connection with the I/O module. Any break in the connection, such as a
module fault or the removal of a module while under power, sets fault bits in the data area associated with the
module.
Rack optimized
Connection
Digital I/O modules only – A rack optimized connection consolidates connection usage between the controller
and all the digital I/O modules in the chassis (or DIN rail). Rather than having individual, direct connections for
each I/O module, there is one connection for the entire chassis (or DIN rail).
Anytime a remote chassis houses I/O modules that use rack optimized connections, the remote ControlNet
communication module connecting these modules to their owner-controller must also use a rack optimized
connection. However, you can mix direct and rack optimized connections to the same remote chassis. For
example, if your remote chassis houses 6 digital I/O modules and your application requires that you use direct
connections for 3 but rack optimized connections for the other others, you can select direct connections for the 3
that require them and rack optimized connections for the other 3. In this case, even though you must use a rack
optimized connection for the remote ControlNet communication module the owner-controller still makes direct
connections with the 3 I/O modules that are configured as such.
You can only make up to 5 rack optimized connections to a single remote ControlNet communication module.
A direct connection is any connection
that does not use the Rack Optimization
Comm Format.
rack optimized connection