Echelon LonTal Stack - Manual (Page 68)

56 Creating a Model File
Declaring a Functional Block
A functional block declaration, by itself, does not cause the LonTalk Interface
Developer utility to generate any executable code, although it does create data
that implements various aspects of the functional block. Principally, the
functional block creates associations among network variables and configuration
properties. The LonTalk Interface Developer utility uses these associations to
create the self-documentation (SD) and self-identification (SI) data in the device
and in its associated device interface file (.xif or .xfb extension).
The functional block information in the device interface file, or the SD and SI
data, communicates the presence and names of the functional blocks contained in
the device to a network management tool.
Network-variable or configuration members of a functional block also have
self-documentation data, which is also automatically generated by the LonTalk
Interface Developer utility. This self-documentation data provides details about
the particular network variable or configuration property, including whether the
network variable or configuration property is a member of a functional block.
Functional blocks can be implemented as single blocks or as arrays of functional
blocks. In a functional block array, each member of the array implements the
same functional profile, but has different network variables and typically has
different configuration properties that implement its network variable and
configuration property members.
Example: The following example shows a simple array of 10 functional blocks.
network output SNVT_amp nvoAmpere[10];
fblock SFPTopenLoopSensor {
nvoAmpere[0] implements nvoValue;
} fbAmpMeter[10];
This functional block array:
• Contains ten functional blocks, fbAmpMeter[0] to fbAmpMeter[9], each
implementing the SFPTopenLoopSensor profile.
• Distributes the ten nvoAmpere network variables among the ten
functional blocks, starting with the first network variable (at network
variable array index zero). Each member of the network variable array
applies to a different network variable member of the functional block
array.
Defining a Network Variable
Every network variable has a type, called a network variable type, that defines
the units, scaling, and structure of the data contained within the network
variable. To connect a network variable to another network variable, both must
have the same type. This type matching prevents common installation errors
from occurring, such as connecting a pressure output to a temperature input.
Type translators are also available to convert network variables of one type to
another type. Some type translators can perform sophisticated transformations
between dissimilar network variable types. Type translators are special
functional blocks that require additional resources, for example, a dedicated
type-translating device in your network.