Echelon Neuron C - Manual (Page 60)

48 How Devices Communicate Using Network Variables
After the device design is complete, you specify connections between network
variable outputs and inputs on different devices. This is discussed in Connecting
Network Variables on page 49. The specification of the desired connections is
used by a network tool to generate the appropriate network addresses. When
these addresses are downloaded into the devices, they ensure that updates sent
by writers reach all of the intended readers.
In the lamp and switch example shown in Figure 6 on page 46, the output
network variables in column 1 are connected to the input network variables in
column 2, as listed in Table 7.
Table 7. Connecting Output Network Variables
Output (device/variable_name) Input (device/variable_name)
switch1/nvoSwitch lamp1/nviLamp
lamp2/nviLamp
switch2/nvoSwitch lamp3/ nviLamp
When a network variable that is a structure is modified by a network variable
writer, the entire structure is updated at the next critical section boundary for all
network variable readers, regardless of whether the structure was wholly or
partially modified.
Network variables can be declared with a single dimension array bound. Each
element of the array is then a separately bindable network variable. See the
descriptions of the poll( ) function, the built-in nv_array_index variable, and the
nv_update_completes, nv_update_fails, nv_update_occurs, and
nv_update_succeeds events in the Neuron C Reference Guide for more
information.
When an element of a network variable that is an array is modified by a network
variable writer, only the modified element is updated at the next critical section.
The maximum size of a network variable is 31 bytes. In the case of a network
variable array, each element is limited to a size of 31 bytes.
The Neuron C compiler includes the SNVT indices (numerical identifiers for the
standard network variable types) in the application image for all network
variables declared as SNVTs, and optionally also includes the network variable
names for all network variables. Network variable names are always included in
the device interface file for a device, but integrators might find them useful when
they lose the device interface file and need to install your device. You can control
these options using the following compiler directives as described in the Compiler
Directives chapter of the Neuron C Reference Guide :
#pragma disable_snvt_si
#pragma enable_sd_nv_names
See the Neuron C Reference Guide for additional information about the syntax
for declaring a network variable.
Examples of Network Variable Declarations
Some sample network variable declarations are the following: