Echelon LNS - Manual (Page 236)

LNS Programmer's Guide 222
Remote Display
Device
Control Device
nvoSetting
nvoSetPoint
Target Network Variables
LNS Application
PC
nviInput
Figure 9.1 Fan-In Connection
When monitoring a fan-in connection, you can monitor the input network variable, the
output network variables, or both. If your application needs to identify the source of an
update, you can create a monitor point for each output network variable, and set the
UseBoundUpdates
property to False, and the
SuppressPollingIfBound
property to
True, when you configure the options for those points. Each time one of the output
network variables is updated, LNS will generate an
OnNvMonitorPointUpdateEvent
for the monitor point associated with the source of the update. If you create a network
variable monitor point for the input network variable on the Network Service Device, you
will also get an update on that point any time any device involved in the connection
sends an update.
Fan-out Connections
Consider a heating system in an office building in which all fans and vents must be shut
off and closed due to a supervisor command given at a central monitoring station. You
could explicitly write a control value to each of the devices in order to shut them down,
but there are two problems with this.
First, it requires knowledge of the maximum number of fan and vent devices to be
controlled, and the application will need send the control value to each one separately.
This will cause at least one message to be sent for each device, which could cause a large
amount of network traffic. Second, it’s an inefficient use of resources for the LNS Server,
which must maintain the network variable configuration, network variable alias, and
self-documentation tables, as well as maintain a record of the application’s external
interface and connections.
An easier, more flexible, and more efficient solution is to connect a single control value
output network variable on the host to each of the input network variables on the fan
and vent devices. This type of connection is called a fan-out connection because a single
output network variable "fans-out" to multiple input network variables. When making
such a connection, it is important that you use an appropriate ConnectDescTemplate
object. The default connection description for all network variables on a Network Service
Device has the AliasOptions property set to lcaAliasForUnicast by default. This
is generally the best setting for fan-in connections to the Network Service Device, as it
may prevent creating a group for each output in the fan-in connection that may also be