NMEA 0183 Basics – How the Marine Communication Standard Works

Learn how NMEA 0183 transfers data between marine devices, the installation rules that apply, and how to convert to NMEA 2000 with Actisense.

NMEA 0183 is a standard developed over 20 years ago to enable communication between marine electronic equipment and navigation computers. It has become the most common method for marine devices to share important data.

What is NMEA 0183?

The standard defines:

• Electrical connections in an NMEA system
• The communication method for data transfer
• The format of the sentences carrying NMEA data

NMEA 0183 is a digital data transfer method that uses binary signals (1s and 0s) to represent information. It has evolved from older standards (NMEA 0180 and 0182), but these are not compatible with NMEA 0183. The newer NMEA 2000 standard is completely different and requires a gateway, such as Actisense NGW-1, for conversion between the systems.

How does communication work?

• Talkers: Devices that send data, e.g., GPS, sonar, compass.
• Listeners: Devices that receive data, e.g., chartplotter, radar, PC.

An NMEA 0183 bus always has one talker but can have multiple listeners. The latest versions (v2 onwards) follow the RS422 standard with low-voltage signaling (+5/0 V), making them compatible with modern equipment. Older devices, however, can use up to ±15 V, which requires the receiving equipment to be opto-isolated to avoid damage and interference.

Important installation principles

• Use shielded twisted-pair cables.
• The shield should only be connected at one end (to the talker chassis) to avoid ground loops.
• All receiving equipment must be opto-isolated according to the NMEA specification.

Data format and compatibility

All NMEA 0183 data is sent as printable ASCII text, allowing it to be displayed in terminal programs like HyperTerminal. Note that NMEA 0183-HS or v3 is not compatible with NMEA 2000. For conversion between these standards, a gateway like Actisense NGW-1 is required.

Challenges with different versions

NMEA 0183 has evolved over time, making connections between older and newer devices complicated. Older devices use ground as a return, while newer devices use differential signaling. Incorrect connection can cause overheating and damage.

The solution – Actisense ISO-Drive

Actisense has implemented ISO-Drive outputs on all new products to provide the necessary isolation and safety. If the ISO-Drive "B" wire is connected to ground, no current will flow, making the system safe even when mixing different manufacturers.

Summary

• NMEA 0183 is an established standard for marine data communication.
• Follow installation rules: opto-isolation, correct cabling, and shielding.
• For conversion to NMEA 2000 – use Actisense NGW-1.
• For secure connection between different devices – choose products with ISO-Drive.