Rockwell Automation 20-750-BNETIP BACnet/IP Option Module - Manual (Page 79)

Rockwell Automation Publication 750COM-UM005B-EN-P - June 2014 79
Glossary
Hold Last When communication is disrupted (for example, a cable is disconnected), the
option module and PowerFlex drive can respond by holding last. Hold last results
in the drive receiving the last data received via the network connection before the
disruption. If the drive was running and using the Reference from the option
module, it will continue to run at the same Reference.
Idle Action An idle action determines how the option module and connected drive act when
the controller is switched out of run mode.
IP Addresses A unique IP address identifies each node on the BACnet/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 BACnet/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 network 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 option module with a DHCP
server, or by manually configuring parameters in the option module. The option
module reads the values of these parameters only at powerup.
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