Raymarine AIS Integration with OpenCPN

[Littlechay]

Originally Posted by nilespf

Littlechay,
Can you comment on my post as of today. Look in this section. Because you use a mux, I'm interested in several 183 data strings overloading the buffers!!!!

Phil

Phil I'm not sure which comments you refer to. I don't see anything from you recently.

The mux I use (shipmodule USB 2) can have at least one port set for real time mode so that data doesn't get lost from something that is updating quickly such as a fast heading sensor. It is easily able to handle data the slow speeds on NMEA after all it's chattering to the computer on USB at 115kb/s. This Mux has four I/O ports. I have one connected to SeaTalk, one connected to the E series display with the AIS and and one feeding NMEA data out to the AIS receiver.

I saw somebody mention here that you can parallel three NMEA ports; which is partially true. You can, usually, distribute a. NMEA output to three receivers but you can't just parallel up transmitters.

Seatalk, you can parallel as many as you will practically need Tx and Rx.

[nilespf]

Littlechay,
Pls go the thread "Route xfers using NMEA0183"

It is a load but bear with it.

Phil

Thanks for responding

[Beausoleil]

Originally Posted by sf-robert

Probably my last comment on this. I subsequently spoke with an independent electronics installer who said that NMEA standards allow up to three parallel connections. I've decided to go ahead with my install as is.

Robert

Robert,

The installer you talked to was somewhat, but not totally, correct. It depends on what electrical interface the vendor used. Originally, it was a "single-ended" transmitter which used ship's ground for the return path, and RS-232 was able to work with it. RS-422 - a differential system with separate transmit and receive returns (i.e. one wire pair for transmit + and -, and a separate pair for receive + and -). If the vendor used RS-422, then one talker could send to four simultaneous listeners out to the full cable distance. If the vendor used RS-232, then it may work, but it depends on the distances and gauge of cabling involved.

In your case, it works today, but if anything changes in your setup in the future, there's no guarantee it will continue to work.

[aluijten]

Originally Posted by Beausoleil

Robert,

The installer you talked to was somewhat, but not totally, correct. It depends on what electrical interface the vendor used. Originally, it was a "single-ended" transmitter which used ship's ground for the return path, and RS-232 was able to work with it. RS-422 - a differential system with separate transmit and receive returns (i.e. one wire pair for transmit + and -, and a separate pair for receive + and -). If the vendor used RS-422, then one talker could send to four simultaneous listeners out to the full cable distance. If the vendor used RS-232, then it may work, but it depends on the distances and gauge of cabling involved.

In your case, it works today, but if anything changes in your setup in the future, there's no guarantee it will continue to work.

If memory serves me right, the 'official' NMEA 2.x specification assumes a RS422 (=current-loop) system. The main reason for this is that it's able to support longer distances and is less prone to interference. As the timing of the signals is identical to RS232 and the electrical specifications are pretty close (12 volt max) many vendors used RS-232 UARTS as these are cheaper and many single-chip processors had the UART integrated.

Cheers,

Arno