Commercial vessel

NMEA 0183: Limitations

The Single Talker Limitation

The NMEA 0183 standard allows any suitably designed marine electronic device to share its gathered information with any other device on a vessel. Unfortunately, this standard has a limiting factor – as it is serial communication, it is a single talker connection. This means that we cannot have two (or more) devices talking/sending data to a connected listener device simultaneously. There is no data, device or address management here, so they would just talk over one another. This would lead to corrupt, lost or invalid data.

The Need for Autoswitching in Marine Electronics

Managing multiple identical devices

For systems that have multiple NMEA devices of an identical type (e.g. two GPS’s or two depth sounders), automatic selection of the highest priority device with valid data is normally a vital requirement. However, the NMEA 0183 standard has no method of automatically switching between different devices, so this requirement is fulfilled using input switching capability within products.

Introducing Autoswitching Solutions

Devices with Autoswitching capabilities

Our PRO-MUX-2, PRO-NDC-1E, PRO-BUF-2 and PRO-NDC-1E2K have Autoswitching capabilities, where the priority can be defined. Our legacy products such as the PRO-MUX-1, NDC-5, and NDC-4 also have Autoswitching ability, which works the same way but this article won’t cover these here.

PRO-BUF-2 Buffer

How Autoswitching Works

Configuring input priority

The Autoswitching process works on the devices by firstly defining the priority of the inputs via the web-based config. This will dictate to the device which input it is to take as the primary source of data, if there are multiple copies of the same data on multiple inputs.

Example scenario

For example, with 2 GPSs connected to a PRO-BUF-2, the primary GPS may be on input #1 and the secondary on input #2. As these devices will be sending the same data, the Autoswitching rules can be set to ignore the GPS data on input 2, unless the data from input 1 stops.

Intelligent Monitoring and Switching

Continuous monitoring

All of our intelligent devices monitor themselves and their respective I/O Ports, meaning they can detect if there is an NMEA 0183 signal present.

Switching mechanism

If the primary GPS suddenly stops outputting, the device will recognise that the primary input has been lost, and will change to the second priority input. However, as the device will still monitor Input 1, once the data returns from the primary GPS and the unit picks this up, after a few seconds for validity and consistency checking, it will then switch back to the primary input.


Enhancing Marine Electronics with Autoswitching

Autoswitching capabilities significantly enhance the reliability and functionality of marine electronics by ensuring seamless and automatic transition between multiple data sources. This not only prevents data loss but also maintains the integrity of the navigational information, thereby contributing to safer and more efficient maritime operations.