Top Line Bus by NKE

Fig.: NKE device with Topline Bus (NKE)

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

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 38400 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 SeaTalk:

  • 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 are no open source implementations for the actual Topline protocol. 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.