User manual
Publication CNET-UM001C-EN-P - November 2005
Configure a ControlNet Module 3-9
Communication Format
The communication format determines:
• what configuration options are available - for example, if the module
uses None, then you do not have to configure an RPI rate on the next
screen.
• what type of data is transferred between the owner-controller and I/O
connected via the communication module.
• what tags are generated when configuration is complete.
• the type of connection between the owner-controller and the I/O
connected via the communication module.
The communication format setting affects the Requested Packet Interval (RPI)
rate on the next configuration screen. This table lists Communication Format
choices.
Communication format does not apply to all ControlNet communication
modules. For example, you do not choose a communication format when
using the 1784-PCIC, 1784-PCICS nor 1788-CNx cards.
Table 3.3 Communication Formats
This Communication
Format Choice
Means And Affects The RPI This Way
Rack Optimized The communication module creates a rack image
and returns I/O data in the rack image to the
owner-controller.
This option is available only for digital I/O modules.
Also keep in mind that diagnostic I/O modules will
not return diagnostic data when you use this format.
You can specify an RPI that is:
• equal to or greater than the NUT.
• in the range permitted by RSLogix 5000
software, for example 2 - 750ms.
When you set the RPI for a remote ControlNet
communication module, we recommend you use a
rate that is a power of two times the NUT.
For example, if your NUT = 5ms, we recommend the
following RPI values:
Listen-Only Rack Optimized
- Choice is not available on
all ControlNet
communication modules.
The communication module creates a rack image
and returns I/O input data in the rack image to the
owner-controller.
The difference between this choice and Rack
Optimized is that the I/O data in the rack image is
returned to a controller that does not control the
outputs but is listening only to its input data.
None No RPI is required The RPI box is grayed out.
NUT = 5m
x 2
0
x 2
1
x 2
2
x 2
3
x 2
4
Optimal RPI
values
5ms 10ms 20ms 40ms 80ms