SeaTalk. Raymarine NMEA Multiplexer

SeaTalk

SeaTalk ® is a proprietary protocol developed by Raymarine ® . This protocol is used for communication between Raymarine navigation instruments like the ST40, ST50 and ST60 series.

To be able to use these instruments with commonly available navigation programs or to feed their data into other non-Raymarine instruments, the SeaTalk data needs to be translated into NMEA.

Even Raymarine's own navigation software, Raytech Navigator, needs this translation.

The MiniPlex can be directly connected to a SeaTalk network. It will translate all SeaTalk data required for navigation into NMEA sentences. Input In 4 can be set to SeaTalk mode

(SeaTalk -> NMEA) and should be connected as shown below:

SeaTalk cable

Red

Yellow

In 4A

In 4B

Multiplexer

Connection to a SeaTalk network

Note that the red and yellow wires are used! The shield of the SeaTalk cable is not connected to the multiplexer.

USB Port

The USB port connects the multiplexer to a computer or a USB hub with the supplied cable. The supplied driver provides a virtual COM port to allow navigation software to communicate with the multiplexer. The USB port is bi-directional: the multiplexer sends NMEA data to the computer and the computer can also send NMEA data back to the multiplexer. This data can be routed to

NMEA Out 1 and NMEA Out2.

The USB port is galvanically isolated from the multiplexer to prevent ground loops and excessive currents that could otherwise destroy the multiplexer or the USB port of the connected computer.

The USB connection supports flow control, which is needed when waypoints and routes are sent from the computer to a GPS through the multiplexer. While normal NMEA sentences are sent at regular intervals, waypoints and routes are sent ‘in one go’ without any pause between these NMEA sentences. This fills up the queue in the multiplexer almost immediately after which the multiplexer discards the remaining waypoints and routes. The GPS now only receives a few waypoints and partial routes.

Flow control prevents this from happening. When the queue in the multiplexer is almost filled, the multiplexer signals the computer to stop sending data. When the queue is sufficiently emptied, the multiplexer signals the computer to continue. This requires a special setting in your navigation software, which is mostly called ‘Flow Control’. This setting can mostly be found in the port settings of your software. Set the Flow Control to Hardware or CTS/RTS. This Hardware flow control is virtualized over the USB connection. Do not use Xon/Xoff flow controls since this uses special characters instead of a (virtual) signal. These characters are not part of the NMEA standard and therefore ignored by the multiplexer.

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