Echelon Neuron C - Manual (Page 23)

Neuron C Programmer’s Guide 11
of this feature in Chapter 3, How Devices Communicate Using Network
Variables , on page 43, and also in the Neuron C Reference Guide .)
An application image for a device created by the Neuron C compiler contains SD
information unless the #pragma disable_snvt_si directive is used. (See the
Compiler Directives chapter of the Neuron C Reference Guide for more
information.)
Data-Driven Compared with Command-
Driven Protocols
Network variables are used to communicate data and state information between
devices. This data-driven model provides a different communication model than
in command-based systems. In command-based messaging systems, designers
are faced with having a large number of commands, specific to each application,
that must be managed, updated, and maintained. Each device has to have
knowledge of every command. This leads to ever-growing command tables and
application code.
With network variables, the command or action portion of a message is not in the
message. Instead, with network variables, this information is in the application
program, and each application program only needs have the knowledge required
to perform its function. A network integrator can add new types of devices at any
time, and connect them to existing devices in the network to perform new
applications not envisioned by the original designers of the devices.
Event-Driven Scheduling or Polled Scheduling
Although the Neuron C language is principally designed to make event-driven
scheduling natural and easy, Neuron C also allows you to construct polled
applications that implement a centralized control application. Chapter 3, How
Devices Communicate Using Network Variables , on page 43, provides further
information on polling.
Low-Level Messaging
In addition to the functional block and network variable communication model,
Neuron C also supports application messages. You can use application messages
– in place of or in conjunction with the network variables approach – to
implement proprietary interfaces to your devices. They are also used for the
L ON W ORKS file transfer protocol. Application messages are described in Chapter
6, How Devices Communicate Using Application Messages , on page 117.
I/O Devices
A Neuron Chip or Smart Transceiver can be connected to one or more physical
I/O devices. Examples of simple I/O devices include temperature and position
sensors, valves, switches, and LED displays. Neuron Chips and Smart
Transceivers can also be connected to other microprocessors. The Neuron
firmware implements numerous I/O models that manage the interface to these
devices for a Neuron C application. I/O models are discussed in detail in Chapter
2,
Focusing on a Single Device , on page 15, and in the I/O Model Reference .