Rockwell Automation Ethernet Design Considerations Reference Manual - Manual (Page 87)

Rockwell Automation Publication ENET-RM002C-EN-P - May 2013 87
Predict System Performance Chapter 5
Use this table to count the total packets/second sent for each EtherNet/IP
communication module in the example system shown on
page 84 .
In addition to the configurable RPI parameter, you control system includes the
Actual Packet Interval (API). The API is the actual time that requested data is
delivered.
The relationship between the RPI and API in your system depends on the
controller initiating the communication. In general, these controller types
calculate the API as follows:
• ControlLogix: API = RPI
• 1768 CompactLogix: API = RPI
• CompactLogix 5370 controllers, SoftLogix™: API = RPI
• 1769-L23E
x, 1769-L3xE: API = 2 n
(where 2
n
is a value that is a power of
2, for example, 2, 4, or 8, that is equal to or faster than the RPI you
configured)
Communication
Module Connection Type Packets/Second
Local 1756-EN2T
communication module Produced tag between
controllers (1 + 1)/20ms = 100
Rack-optimized connections (2 x 1)/20ms = 100
Direct connections (2 x 2)/50ms = 80
Module total packets/second = 280
(1)
(1) A 1756-EN2T/ A module, firmware revision 2.003 has a packet rate capacity = 10000 packets/second. When sending 280
packets/second, the module in the example system uses approximately 3% of its packet rate capacity, well below the recommended
maximum of 90% of the module’s packet rate capacity.
Remote 1756-EN2T
communication module Consumed tag between
controllers 2/20ms = 100
Rack-optimized connections (2 x 1)/20ms = 100
Direct connections (2 x 2)/50ms = 80
Module total packets/second = 280 (1)
IMPORTANT In most cases, you can get data faster than the RPI you configured. This
increased data transmission rate can increase the number of packets to be
more than you expected based on the RPI.
Therefore, the percentage of the EtherNet/IP communication module’s packet
rate capacity used can be slightly higher than expected.