Echelon IzoT Commissioning Tool - Manual (Page 22)

try to talk at the same time. Meaningful transfer of information between devices on a network,
therefore, requires organization in the form of a set of rules and procedures. These rules and
procedures are the communication protocol, which may be referred to simply as the protocol. The
protocol defines the format of the messages being transmitted between devices and defines the actions
expected when one device sends a message to another. The protocol normally takes the form of
embedded software or firmware code in each device on the network. The CNP
is an open protocol
defined by the ISO/IEC 14908-1 standard (defined nationally in the United States, Europe, and China
by the ANSI/EIA 709.1, EN 14908, and GB/Z 20177 standards, respectively).
Device Templates
A device template contains all the attributes of a given device type, such as its functional blocks,
network variables, and configuration properties.
Channels
A channel is the physical media between devices upon which the devices communicate. The Control
Network Protocol is media independent; therefore, numerous types of media can be used for channels
such as twisted pair, power line, fiber optics, IP, and radio frequency (RF). Channels are categorized
into channel types, and the channel types are characterized by the device transceiver. Common
channel types include TP/FT-10 (ISO/IEC 14908-2 twisted pair free topology channel), TP/XF-1250
(high-speed twisted pair channel), PL-20 (ISO/IEC 14908-3 power line channel), FO-20
(ANSI/CEA-709.4 fiber optics channel), and IP-852 (ISO/IEC 14908-4 IP-communication).
Different transceivers may be able to interoperate on the same channel; therefore, each transceiver type
specifies the channel type or types that it supports. The choice of channel type affects transmission
speed and distance as well as the network topology.
Routers
Multiple channels can be connected using routers. Routers are used to manage network message
traffic, extend the physical size of a channel (both length and number of devices attached), and connect
channels that use different media (channel types) together. Unlike other devices, routers are always
attached to at least two channels.
Applications
Every L ON W ORKS device contains an application that defines the device’s behavior. The application
defines the inputs and outputs of the device. The inputs to a device can include information sent on
L
ON W ORKS channels from other devices, as well as information from the device hardware (for
example, the temperature from a temperature sensing device). The outputs from a device can include
information sent on L
ON W ORKS channels to other devices, as well as commands sent to the device
hardware (for example, a fan, light, heater, or actuator).
The application may be in the device when you purchase it, or you may load it into the device from
application files (.nld, .apb, and .nxe extensions) using the IzoT Commissioning Tool.
Applications in devices are divided into one or more functional blocks. A functional block is a
collection of network variables and configuration properties that are used together to perform one task.
For example, a four-port digital input module may have four digital input functional blocks that
contain the configuration properties and output network variable for each of the four hardware digital
inputs on the device.
Network Variables
Applications exchange information with other L ON W ORKS devices using network variables. Every
network variable has a direction, type, and length. The network variable direction can be either input
or output, depending on whether the network variable is used to receive or send data. The network
variable type determines the format of the data.
6 Introduction