Echelon OpenLNS - Manual (Page 289)

OpenLNS Programmer's Reference 252
To read the value of the data point’s source object (the value
of the source object in the OpenLNS database and on the
physical device containing the source object) as an
unformatted numeric value, use the DataPoint object's Read
method, and then read this property. If the AutoRead
property is set to TRUE, the Read method will automatically
be called each time this property is read.
To write to the value stored in this property to the data
point’s source object, set this property to the desired value,
and call the DataPoint object's Write method. If the
AutoWrite property is set to TRUE, the Write method will
automatically be called each time this property is written.
You should note that this property shares memory space with
the FormattedValue and RawValue properties, meaning that
the information contained in all three properties represents
the same value. The only difference between the three
properties is that each of them is formatted differently;
therefore, when you write to the Value property, OpenLNS
will update the values of the FormattedValue and RawValue
properties automatically, to match the updated Value
property.
However, you can only use the Value property to read and
write the values of data points and data point fields that take
single, scalar values, such as SNVT_lev_percent. To read
and write the value of data points containing structures, such
as SNVT_switch, use the FormattedValue and RawValue
properties. You can only write scalar values to the Value
property. If you write a non-scalar value to the Value
property, the LCA, #122 exception is thrown.
If the data point’s source object is a network variable, you
should note that reading the Value property always causes a
poll and returns the resulting response, even if the network
variable is bound to the host or if the Data Server is already
polling. If the Value property is read, and the poll fails, a DS
200 exception is raised, which identifies the error as a
communications error.
If the data point’s source object is a configuration property,
you can use the ValueStatus property to determine if the
value stored in the OpenLNS database for the configuration
property matches the value stored on the physical device. In
addition, the setting of the DataPoint object’s SourceOptions
property affects how OpenLNS accesses the value of the
configuration property (either from the physical device
containing the configuration property, or from the OpenLNS
database). You should also consider that some configuration
properties contain a ConstantAttribute property. If a
configuration property has the constant attribute set, it
marks the configuration property as read-only. If this
attribute is set and you attempt to write to the Value
property, an exception will be thrown. However, in some
cases, you can use the ConstantAttribute property to set or