Allen-Bradley ControlNet Compact GuardLogix 1769, User Manual, Page: 58 / 100

Chapter 4 Control I/O
Direct or Rack-optimized Connections
Logix5000 controllers use connections to transmit I/O data. These connections
can be direct or rack-optimized connections.
Term Definition
Direct connection A direct connection is a real-time, data-transfer link between the controller and an analog or digital I/O module that 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.
A direct connection is any connection
that does not use the Rack
Optimization communication format.
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. Instead of a direct connection for each I/O module, the entire chassis or DIN rail
has one connection.
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 use
both direct and rack-optimized connections to the same remote chassis. For example, if your remote chassis houses six digital
I/O modules and your application requires direct connections for three and rack-optimized connections for the others, you can
choose direct connections for the first three and rack-optimized connections for the second three. 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 three I/O modules configured as such.
Each remote ControlNet communication module is limited to five rack-optimized connections.
Rack-optimized Connection
58 Rockwell Automation Publication CNET- UM001E-EN-P - June 2016