Echelon Neuron C - Manual (Page 182)

162 Network Variable, Configuration Property, and Message Tag Declarations
sd_string ( concatenated-string-constant )
Sets a network variable’s self-documentation (SD) string
of up to 1023 characters. This modifier can only appear
once per network variable declaration. If any of the sync,
polled, or changeable_type keywords are used, then the
sd_string modifier must follow these other keywords.
Concatenated string constants are permitted. Each
variable’s SD string can have a maximum length of 1023
bytes.
The use of any of the following Neuron C Version 2
keywords causes the compiler to take control of the
generation of self-documentation strings: fblock,
config_prop, cp, device_properties, nv_properties,
fblock_properties, or cp_family.
In an application that uses compiler-generated SD data,
additional SD data can still be specified with the
sd_string( ) modifier. The compiler appends this
additional SD information to the compiler-generated SD
data, but it is separated from the compiler-generated
information with a semicolon.
Network Variable Classes (class)
Network variables constitute one of the storage classes in Neuron C. They can
also be combined with one or more of the following classes:
config This variable class is equivalent to the const and eeprom
classes, except that the variable is also identified as a
configuration variable to network tools which access the
device’s interface information. The config keyword is
obsolete and is included only for legacy applications. The
Neuron C compiler does not generate self-documentation
data for config class network variables. New applications
should use the configuration network variable syntax
explained in
Configuration Network Variables on page
164.
const The network variable is of const type. The Neuron C
compiler does not allow modifications of const type
variables by the device’s program. However, a const
network input variable is still placed in modifiable
memory and the value can change as a result of a network
variable update from another device.
When used with the declaration of a configuration
network variable, the const storage class prevents both
the Neuron C application and network tools from writing
to the configuration network variable. The application
can cast away the const-ness of the property to implement
device-specific configuration properties as configuration
network variables. However, because the network
variable is placed in modifiable memory, network variable