Rockwell Automation 842E EtherNet/IP Absolute Encoder User Manual - Manual (Page 16)

8 Rockwell Automation Publication 842E-UM001A-EN-P May 2012
Chapter 3 EtherNet/IP overview
TCP/IP and UDP/IP
EtherNet/IP uses TCP/IP or UDP/IP for communication. (TCP is transmission
control protocol and UDP is user datagram protocol.)
Implicit messaging is used for real-time communication between a programmable
logic controller (PLC) and the encoder in EtherNet/IP. With implicit messaging
a connection is established between exactly two devices within the CIP to
transfer, for example, I/O data such as position or velocity from the encoder to
the PLC. Implicit messaging uses UDP/IP via port 2222. As a result, a fast data
rate is used.
Explicit messaging is used in EtherNet/IP for communication that does not need
to take place in real time. Explicit messaging uses TCP/IP; it is used, for example,
to transfer parameters from the PLC to the encoder.
MAC address
Devices that originate or use data on the network have factory-assigned media
access control (MAC) addresses for unique identification. The MAC address
(MAC ID) consists of 6 bytes. The first three bytes identify the manufacturer.
The last three bytes are unique to the device. An example of a MAC address is
00:00:BC:C9: D7:14.
Communication frame
EtherNet/IP is based on the standard ethernet FRAME. This contains the
ethernet header, the ethernet data and the ethernet trailer. The MAC addresses of
the receiver (destination address) and of the source (source address) are contained
in the ethernet header.
Transmission sequence
Data field Trailer Header
Destination
Address
Source
Address
46...1500 Byte