Actual Packet Interval (Api - Rockwell Automation Allen-Bradley ControlNet 1734-ACNR User Manual

how often to produce the data for that module. For example, if you specify an
RPI of 50ms, every 50ms the I/O module sends its data to the controller
and/or the controller sends its data to the I/O module.
Set the RPI only as fast as needed by the application. The RPI also determines
the number of packets per second that the module will handle on a
connection. Each module has a limit of how many packets it can handle per
second. If you exceed this limit, the module cannot open any more
connections.
Keep in mind that the faster your RPI, the more network bandwidth used. So
only set the RPI as fast as necessary to avoid draining the network bandwidth
unnecessarily. For example, if your application uses a thermocouple module
that has data change every 100ms, do not set the RPI for that node at 5ms
because the network bandwidth is used for data transmissions that are mostly
old data.
You cannot set the RPI to a rate faster than the NUT. The
IMPORTANT
network cannot send data at a rate that is faster than NUT.
When you run RSNetWorx for ControlNet software an Actual Packet Interval
(API) is calculated. The API is equal to or faster than the RPI.

Actual Packet Interval (API)

The API is the actual update rate for a particular piece of data on the network.
ControlNet will set this rate equal to or faster than the RPI, based upon the
binary multiple of the NUT which is the next fastest rate at which a module
can send data. If this can not be done, ControlNet will provide feedback that
the configuration can not be supported.
Understand the Effect of the NUT on the API
The following example illustrates how the NUT affects the API. A module on
the network can produce data only at binary multiples of the NUT to a
maximum of the NUT multiplied by 128. These multiples are referred to as
"rates" on ControlNet. Therefore, in the example of a NUT of 5ms, the
module can send data at the following rates:
ControlNet Overview
Publication CNET-UM001C-EN-P - November 2005
B-5