Top Line Bus by NKE

Fig.: NKE device with Topline Bus (NKE)

Topline is a proprietary serial network protocol from NKE that is used to transmit navigation data and other information on boats and works similarly to Raymarine's SeaTalk with the only difference being that significantly higher data rates are used. Technical data on the transmission protocol cannot be found publicly. Therefore, the specified technical data can only be used with reservations. The topline bus data is transmitted as compact binary data. Topline uses a single-wire connection as the data line for serial data transmission, meaning that they are both sent and received bit by bit over a single line. Implementation is extremely simple because, in addition to the data line, only two additional lines are required for the supply voltage. All devices are simply connected to the data bus in parallel.

Advantages of Topline:

  • Higher data rates: Compared to NMEA0183, Topline can transmit significantly more data due to the compact binary data transmission and the high data rate of 38,400 baud.
  • High data refresh rate of approx. 20 Hz.
  • Bi-directional transmission: Topline offers bi-directional transmission, so data can be both sent and received on the one-wire connection.
  • Reliability: Topline is a reliable network protocol that guarantees that data is transmitted correctly. To do this, checksums are used for the telegrams.
  • Simple Wiring: Units are easy to add to a SeaTalk bus. Most devices use an input and an output port with which the bus can be forwarded to other devices. In this way, many devices can be easily integrated.

Disadvantages of Topline:

  • Proprietary: Topline is a proprietary protocol not supported by other manufacturers. It is only compatible with NKE devices.
  • Expensive connection technology: Topline uses its own proprietary connector format, which is quite expensive.
  • Lack of expandability: Topline's data transmission is designed purely for sensor data. Image data or other large amounts of data cannot be transmitted via Topline.
  • Limited bandwidth: Due to the fixed baud rate of 38400 baud, not any amount of data can be transmitted.

Overall, Topline is a reliable and integrity network protocol for transmitting sensor and navigation data on boats, but it has its limitations, particularly in terms of compatibility and bandwidth. However, NKE has managed to organize the data in such a way that, despite the limited data transmission rate, adequate communication between the devices is possible with a data refresh rate of approx. 20 Hz. NKE devices are designed and optimized for professional sports. NKE has a lot of experience in the field of offshore autopilots in rough conditions and is therefore used on many racing boats.

NKE also offers gateways to NMEA0183 and NMEA2000 in order to be able to use other sensors and devices or to be able to send your own data there. Some NKE Diaplys already include an NMEA0183 gateway. In addition, NKE has made a number of proprietary extensions to NMEA0183 to achieve better performance with their own devices.


There has been an open source implementation of the Topline protocol since 2024 Kristian Jerpetjon.

In addition to the open source implementation, the NKE extensions for NMEA0183 are supported by some open source projects such as SignalK and can also be easily integrated into your own projects. These are special customer-specific NMEA0183 telegrams from NKE.