Rockwell Automation MD65 EtherNet/IP Communication Module - Manual (Page 169)

Glossary Glossary-3
hold last - When communications are disrupted (for example, a
cable is disconnected), the module and MD65 drive can respond by
holding last. Hold last results in the drive receiving the last data
received via the EtherNet/IP connection before the disruption. If the
drive was running and using the reference from the module, it will
continue to run at the same reference.
I/O messaging - Time-critical data such as a Logic Command and
Reference. The terms “input” and “output” are defined from the
scanner’s point of view. Output is transmitted by the scanner and
consumed by the module. Input is transmitted by the module and
consumed by the scanner.
IP addresses - A unique IP address identifies each node on an
EtherNet/IP network. An IP address consists of 32 bits that are
divided into four segments of one byte each. It appears as four
decimal integers separated by periods (xxx.xxx.xxx.xxx). Each “xxx”
can have a decimal value from 0 to 255. For example, an IP
address could be 192.168.0.1.
An IP address has two parts: a network ID and a host ID. The class
of network determines the format of the address
The number of devices on your EtherNet/IP network will vary
depending on the number of bytes that are used for the network
address. In many cases you are given a network with a Class C
address, in which the first three bytes contain the network address
(subnet mask = 255.255.255.0). This leaves 8 bits or 256
addresses on your network. Because two addresses are reserved
for special uses (0 is an address for the network usually used by the
router, and 255 is an address for broadcast messages to all network
devices), you have 254 addresses to use on a Class C address
block.
To ensure that each device on the Internet has a unique address,
contact your network administrator or Internet Service Provider for
unique fixed IP addresses. You can then set the unique IP address
for the module by using a BOOTP server or by manually configuring
parameters in the module. The module reads the values of these
parameters only at power up.
0 1 7 15 23 31
Class A 0 Network ID Host ID
0 1 7 15 23 31
Class B 1 0 Network ID Host ID
0 1 2 7 15 23 31
Class C 1 1 0 Network ID Host ID