Rack Optimized Connections For I/O Modules - Allen-Bradley ControlLogix User Manual

If the module configuration is appropriate for the I/O module found in the
slot, a connection is made and operation begins. If the module configuration
is not appropriate, the connection is rejected. You can view the fault
message on the Connection tab of the module's properties. Module
configuration can be inappropriate for any of a number of reasons (for
example, a mismatch in electronic keying that prevents normal operation).
In this example, the owner controller has three direct connections with I/O
modules in the remote chassis.
Using Direct Connections with I/O in a Remote Chassis
Local chassis
O
I
U
N
T
P
P
U
U
T
T
Owner Logix 5550 ControlNet
Controller
Interface Module
The local controller in this example uses these bidirectional connections:
Connection Type
Logix5550 controller to local I/O module
Logix5550 controller to remote I/O module
Logix5550 controller to remote 1756-CNB module
When you select the communication format for the I/O module, the owner
and listen-only formats are direct connections.

Rack optimized connections for I/O modules

When a digital I/O module is located in a remote chassis (with respect to its
owner), you can select rack optimized communication. A rack optimized
connection consolidates connection usage between the owner and the digital
I/O in the remote chassis. Rather than having individual, direct connections
for each I/O module, there is one connection for the entire chassis.
Slot 1 RPI = 5mS
Slot 2 RPI = 50mS
Slot 3 RPI = 25mS
ControlNet
Module Quantity Connections
2
3
1
Allocating Communication Connections
Remote chassis
O
I
N U
T
P
U P
U
T
T
ControlNet
Interface module
Total
per Module Connections
1
1
1
Total
1756-6.5.3 - December 1999
A-3
I
N
P
U
T
2
3
1
6