Echelon Neuron C - Manual (Page 56)

44 How Devices Communicate Using Network Variables
Major Topics
L ON W ORKS devices communicate with other L ON W ORKS devices through network
variables or application messages. This chapter focuses on network variables,
which provide an open interoperable interface, simplify programming and
installation, and also reduce program memory requirements. Most Neuron C
programs use network variables. Application messages can be used, if required,
as described in Chapter 6,
How Devices Communicate Using Application
Messages , on page 117. Although this manual discusses the two methods
separately, a single Neuron C program can use both network variables and
application messages.
This chapter is divided into the following parts:
• Overview on page 45 summarizes the behavior of devices that are readers
and writers of a network variable, as well as how network variables are
declared. It also describes how network variables on different devices are
connected to each other.
• Declaring Network Variables on page 47 describes the syntax for
declaring network variables, along with related concepts.
• Connecting Network Variables on page 49 describes how network
variable readers are connected to network variable writers. This process
was described in general terms in Chapter 1, Overview .
• Network Variable Events on page 51 describes the following four
scheduling events that are related to network variables:
nv_update_completes, nv_update_fails, nv_update_occurs, and
nv_update_succeeds.
• Synchronous Network Variables on page 53 describes the behavior of
synchronous network variables.
• Processing Completion Events for Network Variables on page 55
describes the two modes of checking for completion events, and the
guidelines for use of these different techniques within an application
program.
• Polling Network Variables on page 56 describes how a reader device can
poll the writer device for the latest value of a network variable.
• Explicit Propagation of Network Variables on page 60 describes how an
application program may exercise explicit control over network variable
propagation, instead of permitting the Neuron firmware scheduler to
propagate network variable updates automatically.
• Initial Value Updates for Input Network Variables on page 62 describes
when and how to manage initial values for input network variables.
• Monitoring Network Variables on page 65 describes special
considerations for implementation of a monitoring device.
• Authentication on page 66 describes how to use authenticated network
variables to increase network security. Authentication allows a reader to
verify the identity of a writer that attempts to update the reader’s value
of the network variable. Authentication can also prevent unauthorized
configuration of a device.