Getting to Know Your NMEA System

History and Overview

NMEA, National Marine Electronics Association, is a non-profit that focuses on marine electronic interface standards and installer training. Currently, NMEA has three main standardized protocols: NMEA 0183, NMEA 2000 and NMEA OneNet. For this blog post, both NMEA 0183 and NMEA 2000 will be the topics of discussion due to OneNet not being widely used since its release in 2020. NMEA 1083 was the first standard introduced in the early 1980s as a way of standardizing marine electronics communication. This standard gave way to NMEA 2000 in 2001, and finally the release of OneNet as mentioned above. Before the establishment of these standards, marine electronic devices from different manufacturers were constrained by proprietary communication protocols. This meant that equipment from one manufacturer was incompatible with that from another, preventing inter-device communication. This quickly became an issue as marine electronics became more sophisticated and the need for integrated systems grew. Creating a huge pain point for users!

Intro to NMEA 0183

NMEA 0183 is known as a serial protocol, a method of communication where data is sent one bit at a time over a single communication line or channel, often used between devices like computers and peripherals or in embedded systems for data transmission. Over the years, since NMEA 0183 release in 1983 it has seen several revisions and updates to accommodate new technologies and the growing demand for higher data transmission speeds and more complex data exchange:

Original (v 1.0) NMEA 0183: Introduced in the 1980s, this version set the framework for serial data communication in marine electronics, using a simple ASCII, serial communications protocol that operates at a baud rate of 4800. ASCII refers to the “American Standard Code for Information Interchange” which is the most common character encoding format for text data in computers and on the internet. Baud rate refers to the rate at which information is transferred in a communication channel. For this example, baud rate of 4800 refers to a serial port capable of transferring a maximum of 4800 bits per second. NMEA 0183 version 1.0 is based on the RS-232 standard, a popular serial communication protocol used in computer and telecommunication equipment. RS-232 was adequate for short-distance communications typical of the configurations at the time. However, it had limitations in terms of transmission distance and was susceptible to electrical noise, which could be problematic in the marine environment, where devices might be spread across a vessel. To overcome these limitations, NMEA 0183 evolved to adopt the RS-422 standard for its physical layer in version 2.0 of the NMEA 0183 protocol.

NMEA (v 2.0) 0183-HS (High Speed): Recognizing the need for faster data transmission as more complex and data-intensive devices became prevalent, the NMEA introduced a high-speed version of the protocol, NMEA 0183-HS or version 2.0, which operates at a baud rate of 38400. This is a significant leap of a factor of eight! That is a massive difference in rate of data transmission from the original NMEA 0183 that is similar to the difference between old dial-up modems to a USB drive (flash drive) or external hard drive. As stated before, NMEA 0183 version 2.0 evolved to overcome the RS-232 limitations by adopting the RS-422 standard. This was significant for several reasons:
Longer Distance Communication: RS-422 supports longer transmission distances (up to 4000 feet), which is beneficial on larger vessels where devices are far apart.
Improved Noise Immunity: RS-422's differential signaling reduces susceptibility to electrical noise, ensuring more reliable data transmission in the electrically noisy environment of a boat.
Higher Compatibility: The transition to RS-422 allowed NMEA 0183 to maintain compatibility with a wider range of devices by facilitating more robust and reliable communication.

The presence of both standards within NMEA 0183 allows it to be versatile and adaptable to various marine installations. It accommodates a wide range of scenarios from small vessels with compact installations to larger ships where equipment may be spread over greater distances. The equipment adhering to the NMEA 0183 protocol effectively employ a "one-to-many" communication model through its talker/listener paradigm, where a single device (the talker) sends data to multiple devices (listeners). This is structurally similar to wireless communications setups used by services like Netflix, where a server (talker) broadcasts data to various devices (listeners) such as smartphones, tablets, and televisions.

While the NMEA 0183 protocol mirrors the structural efficiency of modern streaming services in its "one-to-many" communication model, it is limited by hardware constraints inherent to its design. The protocol primarily uses a single, low-speed serial communication line, which restricts data flow rates and the volume of information that can be transmitted at once. This constraint makes it less suited for applications requiring the transmission of large amounts of data at high speeds.

However, the functional architecture of NMEA 0183 is particularly well-adapted to marine environments where "hard-real time" requirements—where data must be delivered and processed within a strict time constraint to avoid catastrophic failures—are not typically imposed. In marine applications, the emphasis is on the reliable, sequential delivery of accurate navigation and instrumentation data, rather than on the immediate processing of this information.

Intro to NMEA 2000

In 2001, NMEA 2000 was introduced which is based on the J1939 standard, a communication protocol originally developed for heavy-duty vehicles and broader industrial applications. The J1939 standard enhances real-time monitoring, diagnostics, and control over complex systems, facilitating interoperability and reliability among diverse manufacturers and applications across sectors such as automotive, transportation, and industrial machinery.

NMEA 2000 operates on a Controller Area Network (CAN) bus-based protocol representing a significant departure from NMEA 0183. CAN allows for multi-node networks, organizes data into Parameter Groups (PGs), and employs standardized messages for a variety of data types. CAN allows for higher data transmission rates, simpler cabling, and more complex and flexible data exchange among a wide array of devices. The NMEA 2000 protocol specifies how messages are transmitted between electronic devices, including the message format, message timing, and message priority. It also defines how devices can identify themselves on the network and how they can request information from other devices. NMEA 2000 allows for data to be sent and received between devices over a single network cable or better known as a “backbone” cable. This system allows for streamlined integration of new marine devices.

NMEA 2000 Standard: This is the original version of the NMEA 2000 standard, also known as NMEA 2000 version 1. It operates at a data transmission speed of 250 kilobits per second (Kbps) and is suitable for most marine applications where moderate data rates are sufficient.
NMEA 2000 High Speed: The NMEA 2000 High-Speed specification, also referred to as NMEA 2000 version 2 or NMEA 2000 HS, supports faster data transmission speeds compared to the standard version. It operates at a speed of 1 megabit per second (Mbps), which is four times faster than the standard version. The high-speed specification is designed for applications that require higher data throughput, such as advanced instrumentation and rapid updates of large datasets. It is important to note however that modern wifi systems have network speeds of over can deliver theoretical speeds of up to 1201 Mbps (for single stream) or up to 4804 Mbps (for eight streams) on the 5 GHz band. This illustrates that a system based off of a wifi standard rather than NMEA protocols would have a significant advantage in data transmission.
NMEA 2000 Next Generation (NG): The NMEA 2000 NG specification is an evolution of the standard and high-speed versions, introducing additional features, improved data management, and enhanced network performance. It builds upon the existing NMEA 2000 protocols while offering advancements in data processing, security, and compatibility with modern marine electronics.

NMEA 2000 has become the standard communication protocol for marine electronics due to its role of modernizing and streamlining enhanced connectivity, data sharing, diagnostic capabilities, and overall system integration for a safer and more enjoyable boating experience. Despite the introduction of NMEA 2000, NMEA 0183 remains in use due to its simplicity and the vast number of devices that still support it. Trident North’s setup seamlessly incorporates both NMEA 0183 and NMEA 2000 standards, and is connected via Wi-Fi. This allows us to integrate the Marine standards with any other user-defined sensors into one cohesive system. This adaptability provides our system with a competitive edge, enabling us to create a solution that is not only tailored to our needs and cost-effective but also offers the potential for unlimited future expansion.

NMEA 0183 vs. 2000

Now that we have some background regarding the NMEA 0183 and NMEA 2000 systems, let's dive deeper into the differences between the two protocols. Table 1 below illustrates a broad overview of the fundamental differences of each standardization.

Table 1: NMEA 0183 vs. NMEA 2000 (1)

NMEA 0183 is recognized as a protocol with a single talker, multi-listener configuration. In this context, a "talker" is a device that sends out data, such as a GPS, Depth Sounder, Knot Meter, or Compass. These devices provide essential navigational and operational data to other devices on the network. "Listeners" are devices that receive this data and use it to perform specific functions; for example, Chart Plotters use data from GPS, Radars use data from Sonar, and PCs might receive data from multiple talkers. Talkers are essentially outputs transmitting NMEA data, while listeners are inputs that consume the data.

Understanding this dynamic is crucial because NMEA 0183 and its successor, NMEA 2000, differ significantly in how they handle network capabilities for talkers. In the NMEA 0183 system, each cable can only support one talker. If a scenario requires multiple talkers on the same cable, a multiplexer is needed to combine their data streams, facilitating coordinated communication among devices.

For clarity, consider the differences in the NMEA protocols as depicted by diagrams from Actisense. NMEA 0183 has two notable versions: version 1.0, which adheres to the RS-232 standard and is termed a "single-ended" talker because it uses one signal wire and a common ground. This is contrasted with version 2.0, which complies with the RS-422 standard, known as a "differential" talker due to its utilization of two signal wires. This distinction highlights the evolution in NMEA 0183's capability to handle data transmission more effectively, accommodating the increasingly complex requirements of modern marine electronics. Equipment typically labels outputs as "Data" or "TX," with "B" often used as the ground line.