The NMEA Output will transmit SeaTalk data such as Depth, Boat Speed and Wind Speed. The NMEA Input will receive GPS data and re-transmit onto the SeaTalk network. The ST60 Multi Instrument has a NMEA input and a NMEA output. They communicate with each other and are connected to the Autopilot via a SeaTalk network. Raymarine ST60 Boat Instruments - These are the Boat Speed, Wind and Depth Instruments. The output is either via USB, NMEA 0183 (38,400 Baud) or NMEA 2000. The device will accept NMEA 0183 (4,800 Baud) or NMEA 2000 and will multiplex (re-transmit) this data into its USB output. Vesper XB-8000 AIS - This outputs GPS data (Location, Speed Over the Ground, etc.) and AIS data (Positions of other vessels). On Alba, there are six devices with data interfaces: Raymarine do not publish the technical details of SeaTalk, but there is an excellent technical description of SeaTalk on the following website: Raymarine produces an interface to pass data between the two systems and also many Raymarine chart plotters input and output NMEA 0183 data The data messages and the electrical wiring is different to NMEA, so the two systems are not directly compatible. The three wires are contained in proprietary cables with D-type connectors making the connection much simpler than NMEA. In addition to the data wire, there is also a +12V wire and a ground wire. Each device listens on the data line and is allowed to transmit its data when there is a long enough pause in the communication from other devices. In SeaTalk 1, the devices are daisy-chained, so that data flows from one device to the next in a chain. SeaTalk-NG is a proprietary extension of NMEA 2000. There have been later versions of the protocol with different wiring, the latest of which is SeaTalk-HS.
#Garmin nmea 2000 wiring diagram serial#
SeaTalk 1 is a proprietary network designed by Raymarine, which is a serial data protocol similar to NMEA, but there is only one "Data" wire and the information flows in both directions along the wire. (Device 1 should ignore it's own messages, but some devices will get confused when receiving their own messages, so the connection into Device 1 may have to be removed.)
However, if Device 2 is acting as a "multiplexer" then the output of Device 1 will be combined with the output from Device 2 and sent to Device 3. you could not connect the outputs from Device 1 and Device 2 directly to Device 3. Note that without using a "multiplexer" there should only be one transmitter going into a NMEA input. There are four wires - data going out of a device is transmitted on one pair and data is received along another pair, there is also a ground (earth) wire. To put this into simple English, each device on the NMEA network can transmit and/or receive data along twisted pairs of wires. For example, the GPRMC sentence contains Latitude, Longitude, Speed Over the Ground and Track direction. The NMEA 0183 standard defines the contents of each data sentence type, so that all listeners can read sentences accurately.
Common values are 4,800 baud and 38,400 baud. The speed that data is transmitted is known as the Baud Rate and is the number of pulses per second. Through the use of "multiplexers", data from multiple devices can be combined into one data stream and fed into other devices.
The NMEA 0183 standard uses a simple ASCII, serial communications protocol that defines how data is transmitted in a "sentence" from one "talker" to multiple "listeners" at a time. This is done to minimise data corruption from stray electrical noise. One of the wires in each twisted pair carries a positive voltage signal and the other carries a negative voltage signal. Physically, the wiring is four wires made up of two twisted pairs - one pair for data output and one pair for data input. Interfacing to a computer is usually done via an RS232 to USB interface. The electrical standard is RS422, although most hardware with NMEA-0183 outputs are able to drive a single RS232 port. (It is slowly being phased out in favour of the newer NMEA 2000 standard, but this is not used on Alba.) NMEA 0183 is an electrical and data specification for communication between marine electronics such as echo sounder, autopilot, GPS receivers and many other types of instruments. The chart plotter and radar were bought in 2015 and are connected together using SeaTalk-HS. Alba has electronic equipment that predominantly interfaces using SeaTalk 1 and NMEA 0183.
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