Echelon LNS - Manual (Page 248)

LNS Programmer's Guide 234
properties when it is absolutely necessary. For an overview of configuration property
access performance, see Performance Considerations on page 240.
Generally, you should perform configuration property management using the
ConfigProperty
objects stored in the LNS database, rather than by writing to the
configuration property value directly via network variable writes. If a configuration
property is implemented as a configuration network variable and is then modified via a
network variable write, the value of the configuration property on the physical device
will be updated. However, the value stored in the LNS database will not be updated.
Then, if the
DownloadConfigProperties()
method is called, the unsynchronized
values in the LNS database will be downloaded to the device, and the changes made to
the physical device will be lost. As a result, you need to make sure that the values of the
configuration properties on the devices on your network are synchronized with the values
stored in the LNS database for those configuration properties.
To facilitate this, LNS Turbo Edition features the ability to access configuration
properties via
DataPoint
objects. To do so, the LNS application must first call the
ConfigProperty
object’s
GetDataPoint()
method. The
GetDataPoint()
method
takes an
options
element, which you can use to determine how the value of the
configuration property in the LNS database and in the physical device will be affected by
changes made to the
DataPoint
object. The following sections describe how you can use
the
GetDataPoint()
method.
NOTE: Prior to LNS Turbo Edition0, the ConfigProperty object’s Value property was
provided for single read and write operations to configuration properties. Note the Value
property is deprecated and only supported for backwards compatibility.
Device-Specific Configuration Properties
Some configuration properties are designed to be modifiable by multiple distributed
sources, instead of solely by a central network manager. They are designated as such by
the device-specific flag. The value of a device-specific configuration property should
generally be read from the device itself, and not from the LNS database. However, LNS
does not enforce this restriction. The LNS application must decide whether to use the
device-specific configuration property in the device, or in the database. You can use LNS
to determine if a configuration property is device-specific by reading its
DeviceSpecificAttribute
property. If a configuration property is device-specific, the
DeviceSpecificAttribute
property will be set to True.
By default, the values of device-specific configuration properties will be read from the
device. The values of non-device specific configuration properties will be read from the
database if the values are available there, and from the device if they are not. You can
set the
SourceOptions
property to
lcaDataSourceOptionsfromDevice
at any time
to read configuration property values from the device rather than the database, or to
lcaDataSourceOptionsDatabaseOnly
to specify that the values must be read from
the database, independently of the device-specific flag.
To provide full support of device-specific configuration properties, the
UploadConfigProperties()
and
DownloadConfigProperties()
methods have
options to that allow you to upload or download device-specific configuration properties
separately from non-device specific configuration properties. These options are the
lcaConfigPropOptExcludeDeviceSpecific
and
lcaConfigPropOptOnlyDeviceSpecific
flags. They can be combined with the other
download/upload flags. For example, to download non-device specific configuration