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Old 10-06-2016, 19:28   #1
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Garmin AIS Communication Issues

I have a Garmin 540s chart plotter and this year I decided to add an AIS receiver to my electronics. I purchased a McMurdo M15s and installed it along with my radio. The radio is a Uniden UM525 with DSC and it communicates with the Garmin on the Garman communications channel 1 at 4800 bps. This has been working for several years.

When installed the AIS I planned to have it communicate on channel 2 of the Garmin and wired it that way. There is a piece of CAT5 cable that connects the two devices. Upon installation, I could see that the AIS was receiving traffic but no traffic was showing up on the Garmin’s AIS list. Thinking that I may have cross wired something in the CAT5 connecting cable, I removed the radio from the connecting block I am using and put the AIS on channel 1, which I know is working. The AIS still did not show up on the Garmin. I also went into the M15s using the McMurdo PC software and set the port speed to 4800 and set the port speed in the Garmin to 4800 in both ports.

One item I do not understand is the difference between RS232 and RS422 in the McMurdo. The McMurdo manual shows the RS422 interface as having positive and negative transmit and receive leads. RS232 has a positive transmit and receive lead but the negative leads are just a ground. The Garmin only has five leads, positive transmit and receive on two channels plus a common neutral/ground. I assume therefore that the Garmin is using an RS232 interface. However, in the McMurdo, there is no setting to select RS232 or RS422. You can only select the port’s speed, not its type. How does one tell the McMurdo to use the RS232 interface? Any other ideas as to why this is not working?
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Old 10-06-2016, 19:49   #2
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Re: Garmin AIS Communication Issues

Usually AIS info is at baud rate 38400, not 4800. Try resetting the baud rates for the ports you are using.
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Old 10-06-2016, 21:58   #3
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Re: Garmin AIS Communication Issues

you need to run ais at 38,400. and set garmin to that speed. you may also need to turn on the ais layers on the garmin chart.
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Old 11-06-2016, 12:44   #4
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Re: Garmin AIS Communication Issues

OK. I'll look into both suggestions though I started at 38,800 and that did not work and I have not seen any settings for an AIS layer in the charts of this Garmin model. I'll get back.
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Old 11-06-2016, 20:24   #5
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Re: Garmin AIS Communication Issues

you defiantly need to change the garmin speed. it'll be in the communication menu. for nmea 183 pp


port speeds
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Old 12-06-2016, 04:51   #6
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Re: Garmin AIS Communication Issues

Thank you for your responses. I'll have a chance to work on this tomorrow. I've read through the Garmin manual and I see a couple of items I need to take a look at.
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Old 12-06-2016, 08:45   #7
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Re: Garmin AIS Communication Issues

The ais disappear on Garmin 7212 when I overlay my radar. Garmin techs came on board and couldn't understand it, sent a pic to Garmin development. That was last summer and the last I heard from Garmin.

Sent from my SM-N900V using Cruisers Sailing Forum mobile app
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Old 14-06-2016, 17:26   #8
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Re: Garmin AIS Communication Issues - Solved

I took the time to read through the PDF version of the manual for my 540s Garmin chartplotter. This document is more comprehensive than the paper copy I keep on board the boat. By searching the term "AIS", I was able to find several references that seemed to clear up how to enable the AIS feature, but I found that once I was on the boat again, I could not find the settings I was looking for in the actual configuration settings of the unit.

Since I was bringing a laptop with me anyway to configure the AIS, I put a copy of the PDF on it before leaving for the boat. I read through this again and came to the not-so-obvious conclusion that the only way to get to the AIS configuration settings is to reset the unit to its factory default settings and restart it. Upon restarting a whole new set of configuration settings appear, including the sought after AIS settings. This is actually in the form of how you want to use the communications ports, but as soon as I set Com-1 to DSC and Com-2 to AIS, the AIS proximity alarm starting beeping as there were several boats transmitting nearby. AIS was working!

It looks like I had the cross wiring right all along and the signaling for the AIS is set for NMEA high speed (38,400). I still need to learn the details of using AIS and DSC together, but getting the instruments working properly is a good first step. Thank you everyone for your comments. They did help guide me to the ultimate answers I needed.
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Old 14-06-2016, 18:13   #9
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Re: Garmin AIS Communication Issues

AIS 38500

rs 422 four wire layout (two of the four only used, if one way)
rs 232 three cable layout (two of the three used for one way)

rs 422 very common on AIS units (esp. transducers)
rs 232 more common for short wire runs, lower baud rates, and generally cheaper equipment

rs 232 has gnd common for data in and data out.

rs232 and 422 do not talk to each other unless you use an interface piece (rs232/422 adapter)

You can test somewhat by splitting the AIS out data by feeding it into a PC first. Any PC nmea monitor will show the flow.

Have fun. It is a 232 / 422 issue very likely. Easy to solve.

Cheers,
b.
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