NMEA 2000
What You Need To Know About the Industry’s Powerful Network Standard
BY STEVE SPITZER, NMEA TECHNICAL DIRECTOR
NMEA 2000 was created to meet a wide
variety of needs. It is important to note
that it was produced by the marine electronics industry as an industry open
standard, not by one manufacturer.
Development began in 1994 with the
NMEA 2000 Standards Committee.
More than 40 academic, industry and
international organizations took part,
including Kansas and Oklahoma State
Universities, the networking and computer industry (Sun Microsystems), US
Coast Guard Research & Development
Centre and CAN manufacturers such as
Kvaser and Vector Can Tech, along with
marine electronic companies from
around the world.
It was then BETA tested for 18
months under NMEA guidance by
Furuno USA, JRC, Litton Marine,
Navionics, Northstar, Raymarine,
Simrad, Teleflex, Trimble and Wood
Freeman. The National Marine Elect-
ronics Association completed and
released NMEA 2000 in October 2001.
Some of the key requirements were:
• message prioritization
• proven, robust, safe
• data creation simplified
• certification testing
• standard cables and connectors
• bi-directional, multi-talker/multi-
listener, multi-master, no single
controller
• single-channel serial bus, which
operates at 250 Kbits/sec (50 times
faster than 0183)
A single network cable replaces a
myriad of cables typically used in today’s
interconnections. The NMEA 2000 network accommodates navigation equipment, electrical power generation and
distribution systems, engines and other
machinery, piloting and steering systems, fire and other alarms and controls.
Data, commands and status all share the
same cable at speeds 50 times greater
than the NMEA 0183 serial interface.
NMEA 2000 is self-configuring; no set-up is required and no master controller
is needed. Equipment may be added or
removed without shutting down the network.
Based on CAN
(Controller Area Network)
Key to NMEA 2000 is an integrated circuit implementation of a network access
protocol commonly known as CAN
(Controller Area Network). CAN was
developed by Intel and Robert Bosch
GmbH in the mid-1980s in the specification and development of integrated
circuits for a device that would provide a
serial communications protocol to support distributed real-time control applications. CAN was designed to function
in electrically noisy environments, to be
robust, reliable, and have a predictable
delivery time for any information being
moved on the network.
CAN’s initial objective was to provide
a robust solution for automotive applications that included high-speed networking as well as low-cost wire multiplexing. CAN was originally intended for
real-time engine and transmission control, for anti-skid braking systems, and
to replace wiring body components.
CAN is now a ubiquitous network protocol used by a myriad of industries,
such as automotive, agriculture, robotic,
factory automation and others where a
vigorous real-time deterministic protocol is required for absolute message
delivery.
The marine electronics industry
utilized CAN as the basis to develop the
bi-directional multi-transmitter/multi-receiver instrument network to interconnect marine electronic devices – NMEA
2000.
How it Works
The NMEA 2000 network allows multiple electronic devices to be connected
together on a common channel for the
purpose of easily sharing information.
Because it is a network and because multiple devices can transmit data, a more
comprehensive set of rules is required
that dictate the behaviour of the members of the network. CAN automatically
provides some of these rules, mostly for
control of access to the network, packet
transmission and error detection.
One important requirement is to provide for mission-critical data with multiple priorities. This requirement is
addressed through proper application of
multiple message priority levels.
Message priorities are reflected in message identifier assignments, device classification codes, and application-depen-dent message priority bits. All certified
NMEA 2000 devices must demonstrate
the ability to adhere to NMEA 2000
requirements through automated software testing and validation. A product
that passes certification testing will be
capable of supporting mission-critical
operations, even if that product in and of
itself is not related to the mission-critical
functions being conducted on the
NMEA 2000 backbone.
The NMEA 2000 Standard defines all
of the pertinent layers of the
International Standards Organization
Open Systems Interconnect (ISO/OSI)
model, from the Physical Layer to the
