Echelon LNS - Manual (Page 39)

LNS Programmer's Guide 25
and the value of the SCPTnvType configuration property will be updated to inform the
device of the network variable type.
For ideal performance, an application using versions of LNS prior to LNS Turbo Edition
should modify the SnvtId property first, and then the SCPTnvType configuration
property. The operations should be performed in the same transaction. However,
applications using LNS Turbo Edition and later should use the TypeSpec property for all
network variable type changes, since this method supports user-defined types and
standard types, is more efficient, and does not require the application to explicitly
manage the SCPTnvType configuration properties.
Compatibility Case 2 – Devices That Support Old and New Style
NV Type Management
Consider a device that supports both the old SI/SD method of network variable type
modification, and can read the SCPTnvType configuration property. Such an application
should:
1. Define the default value of the network variable with its type_category
set to NVT_CAT_NUL.
2. Honor the SI/SD value if the configuration property’s type_category is
NVT_CAT_NUL (i.e. use the SNVT_ID stored on the device). Otherwise,
honor the value of the configuration property.
First, consider the device being managed by an application using an LNS version prior to
Turbo Edition that does not update the SCPTnvType configuration property. Changes to
the network variable type will result in updating the SI/SD data on the device. The
application device will then use the SI/SD information because the value of the
SCPTnvType configuration property value will remain invalid.
Now consider how an upgrade to Turbo Edition will affect this application. LNS will
recognize that the configuration property value is invalid (its type_category set to
NVT_CAT_NUL) or unknown, so LNS will continue to use the SI/SD to inform the device
of the network variable type. A replace or recommission operation on the device will set
the SI/SD information to be updated, based on the type assigned to the network variable
in the LNS database. Changing the network variable type to a standard type in the LNS
database will cause LNS to update the SCPTnvType configuration property
automatically and to stop updating the SI/SD data for the network variable. The
application will honor the configuration property. Changing the network variable type to
0 (indicating a non-standard type) will cause LNS to update the SCPTnvType
configuration property with a category of NVT_CAT_NUL, and set the SI/SD value in the
physical device to 0.
Next, consider a device being managed by an application that uses the SCPTnvType
configuration property properly, using an LNS version prior to Turbo Edition. In this
case, the application device honors the value of the SCPTnvType configuration property,
since it is valid. When upgrading to LNS Turbo Edition, the LNS database conversion
will recognize that the configuration property is valid, and will update the network
variable type based on that value. A subsequent replace operation will not update the
SI/SD data for that network variable.