Rockwell Automation 1794-OB16D FLEX I/O Diagnostic Modules User Manual - Manual (Page 63)

Publication 1794-UM061A-EN-P - July 2006
Configure Your Adapter and Digital Modules on a ControlNet Network 61
Direct or rack-optimized connection
Logix5000 controllers use connections to transmit I/O data. These
connections can be direct connections or rack-optimized connections.
direct connection A direct connection is a real-time, data transfer link between the controller and an I/O module - analog or digital. In
some cases (for example, with some modules) 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 chasis (or DIN rail).
Any time 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
the 3 that require them and rack-optimized connection for the 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.