Terminology » ISOBUS vs NMEA 2000 vs SAE J1939: Key Differences

ISOBUS vs NMEA 2000 vs SAE J1939: Key Differences

automotive isobus nmea2000 nmea j1939 protocols

Introduction: While ISOBUS, NMEA 2000, and J1939 are all communication protocols built on the Controller Area Network (CAN) bus, they are tailored for different industries and have distinct functionalities. At their core, they share a common ancestor in CAN, but have evolved to meet the specific demands of agriculture, maritime, and heavy-duty vehicles, respectively.

SAE J1939

The established protocol for heavy duty and commercial vehicles, including trucks, buses and construction equipment.It is also used in other sectors like mining, military and power generation. J1939 primarily focuses on the communication of engine data, diagnostics, and control information between electronic control units (ECUs).

ISOBUS (ISO 11783)

The standardized communication protocol for the agricultural and forestry industries. Its main goal is to ensure “plug and play” compatibility between tractors and implements (like sprayers, seeders, and balers) from different manufacturers. This allows a single display in the tractor’s cab, known as a Virtual Terminal, to control any connected implement.

NMEA 2000

The standard for the maritime industry, used on boats, ships, and yachts. It enables seamless communication between a wide range of marine electronics, such as GPS receivers, autopilots, depth sounders and engine instruments.

Evolution

All three protocols are based on the CAN bus, which handles the physical and data link layers of communication.However, their higher level protocols, which define the “language” spoken on the network, are distinct.

The relationship between them is evolutionary:

  • SAE J1939 was developed first by the Society of Automotive Engineers.
  • ISOBUS was derived from J1939, adapting it for the specific needs of agriculture. It maintains a high degree of compatibility with J1939.
  • NMEA 2000 also references parts of J1939 and ISOBUS, tailoring the messaging for the marine environment.

Key differences

FeatureJ1939ISOBUSNMEA 2000
IndustryHeavy Duty & Commercial VehiclesAgriculture & ForestryMaritime
Primary GoalVehicle control and diagnosticsInteroperability between tractors and implementsInteroperability of marine electronics
Key Functionalities1. Engine Control and Monitoring: Transmits real time parameters like RPM, torque and temperature 2. Standardized Diagnostics: Provides diagnostic codes for maintenance and repair. 3. Fleet Management Telematics: Gathers data for optimizing fleet operations.1. Virtual Terminal (VT): A single display for all implements. 2. Task Controller (TC): Manages and documents tasks like seeding and spraying. 3. Section Control: Automates implement sections to avoid overlaps.1. Multi-Function Displays (MFDs): Centralized display of data from various sensors. 2. Autopilot Integration: Uses GPS and wind data for navigation. 3. Engine and Fuel Monitoring: Real time data on engine performance.
ConnectorsDeutsch connectors are commonly used in the heavy-duty vehicle industryStandardized 9-pin connectors designed for harsh agricultural environments.Micro-C connectors designed for the marine environment to resist saltwater corrosion
Data Messages (PGNs)Defines a standard set of Parameter Group Numbers (PGNs) for vehicle dataIncorporates J1939 PGNs but adds specific messages for agricultural tasks.Defines its own set of PGNs specific to marine applications, but they do not overlap with J1939 PGNs
Transport ProtocolsPrimarily uses broadcast messages for real time data and a defined transport protocol for multi packet messagesUses extended transport protocols for larger data transfers, like uploading object pools to the Virtual Terminal.Employs a “Fast Packet” protocol for efficient transmission of medium-sized data payloads.

Conclusion: Comparing ISOBUS, NMEA 2000, and SAE J1939 reveals how each protocol optimizes communication within its target domain i.e. farming, marine or heavy duty vehicles. Recognizing their similarities and unique features supports better system compatibility, performance and network design decisions.