NMEA Wiring

Gibsonsky

Member
Joined
Jul 26, 2020
Messages
16
Reaction score
1
Points
3
Age
51
Model
Fisherman 204
Bought a 1988 Grady that came with an ICom ICM422 radio. Finally got an antenna for it and thats all good. Was wondering about connecting to my Garmin GPSMAP 742xs. Is it just a matter of connecting the two in and out leads from the radio?
Specs say NMEA0183 ver 2.0 or 3.01. Oh, the wires for the ext. speaker, public address, and NMEA are clean cut, not sure if thats how it was originally.
 

seasick

Well-Known Member
Joined
Aug 19, 2008
Messages
6,619
Reaction score
711
Points
113
Location
NYC
In addition to connecting the wires correctly ( if leads are reversed, the link won't work) you will need to configure the port on the plotter and perhaps the radio. You will have to look at the manuals. The key parameter is port speed but there are others that may or may not need tweaking.
 
Last edited:

Gibsonsky

Member
Joined
Jul 26, 2020
Messages
16
Reaction score
1
Points
3
Age
51
Model
Fisherman 204
If I get one of these cables "Garmin NMEA 2000 backbone/drop cable" do I just cut the male end of it and hard wire the correct wires?
 

seasick

Well-Known Member
Joined
Aug 19, 2008
Messages
6,619
Reaction score
711
Points
113
Location
NYC
If the interface is 0183, Nmea 2000 won't help, its a different beast altogether.
 

SkunkBoat

Well-Known Member
Joined
Oct 12, 2017
Messages
2,396
Reaction score
680
Points
113
Location
Manasquan Inlet NJ
Website
www.youtube.com
Model
Express 265
You need the manuals for both the VHF and the 742. identify the correct pairs to connect what you are trying to share. I'm guessing you are connecting gps data to the DSC VHF? Or are you connecting AIS data from the VHF to the 742? or something else?
 

Hookup1

GreatGrady Captain
Joined
Oct 16, 2007
Messages
849
Reaction score
176
Points
43
Location
Cape May, NJ
ICOM 422 is a NMEA183 single ended interface. The Garmin is a NMEA 183 differential interface.

ICOM NMEA-IN lead is red. >>>. Garmin NMEA-OUT+ Blue. NMEA-OUT- Grey is not connected.
ICOM NMEA-OUT lead is white. >>> Garmin NMEA-IN+ Brown. NMEA-IN- Violet is not connected.


Select instruction manual download. Page 35.

nmea2to1.png
 

Gibsonsky

Member
Joined
Jul 26, 2020
Messages
16
Reaction score
1
Points
3
Age
51
Model
Fisherman 204
Thanks for providing your knowledge and info... Im only beginning to try and understand how NMEA works.
 

seasick

Well-Known Member
Joined
Aug 19, 2008
Messages
6,619
Reaction score
711
Points
113
Location
NYC
For those who have never connected NMEA 183 devices, I am sure you said " How hard can it be, it's only 3 (really 2) wires.............
 

SkunkBoat

Well-Known Member
Joined
Oct 12, 2017
Messages
2,396
Reaction score
680
Points
113
Location
Manasquan Inlet NJ
Website
www.youtube.com
Model
Express 265
You have a previously owned DSC VHF. For you to use DSC you need an MMSI #. It has to be YOUR MMSI#. If the previous owner entered his MMSI# then either you can get him to transfer that number to you or you might have one chance remaining to enter your own. If it has already been reprogrammed once you are SOL.

You need GPS data for DSC to be useful. It will transmit your position in DSC calls (I don't know ANYONE who uses DSC calling) and most importantly, when you press the DISTRESS button. Your VHF can get GPS data from your 742 using the NMEA 0183.
The M422 does not have a Baud rate setting that I can find so assume it is 4800 baud

If you don't hookup GPS and/or you can't enter your own MMSI, your VHF will operate fine but you will not be able to use the Distress button or DSC.

If those things are important to you then you might consider a new VHF with built-in GPS.


Screen Shot 2021-07-21 at 1.40.19 PM.png


Screen Shot 2021-07-21 at 1.33.48 PM.png
 

Gibsonsky

Member
Joined
Jul 26, 2020
Messages
16
Reaction score
1
Points
3
Age
51
Model
Fisherman 204
I checked the VHF settings and there's no registered MMSI #. So I acquired my own and will input the #. Then i'll try my best to hook up the two wires (fingers crossed for extra credit) lol
 

Gibsonsky

Member
Joined
Jul 26, 2020
Messages
16
Reaction score
1
Points
3
Age
51
Model
Fisherman 204
Able to input MMSI #. Hooked up ICOM red to GARMIN blue, and ICOM white to GARMIN brown. No location/GPS data between the two.
Anything i'm missing ?
 

seasick

Well-Known Member
Joined
Aug 19, 2008
Messages
6,619
Reaction score
711
Points
113
Location
NYC
I think that the data flow is one way only. You would need the red wire on the icom connected to brown it seems on the Garmin, You also must connect the signal ground which is the shield (braid) of the wire bundle. Connect braid to braid between the two devices. t I suspect you need to configure the interface in either or both devices. At a minimum, you need to verify the baud rate, maybe some additional params.. It's been a long time since I wired one of those. Like I said, it's only two wires, how hard can it be:)
 
Last edited:

SkunkBoat

Well-Known Member
Joined
Oct 12, 2017
Messages
2,396
Reaction score
680
Points
113
Location
Manasquan Inlet NJ
Website
www.youtube.com
Model
Express 265
Able to input MMSI #. Hooked up ICOM red to GARMIN blue, and ICOM white to GARMIN brown. No location/GPS data between the two.
Anything i'm missing ?
Does the red wire on the M422 have a braided shield? If so, connect it to the Black ground wire of the M422.

I'm going to ignore the white wire and inputs to the Garmin because you are probably never going to make/review DSC calls using the Garmin...

Your Garmin may need to be configured to output GPS data sentences on port
Look in your manual for similar to this...

Configuring NMEA 0183 Output Sentences
You can enable and disable NMEA 0183 output sentences.
Select Settings > Communications > NMEA 0183 Setup > Output Sentences.
Select an option.
Select one or more NMEA 0183 output sentences, and select Back.
Repeat steps 2 and 3 to enable or disable additional output sentences.
Screen Shot 2021-07-23 at 4.46.37 PM.png

Setting the Communication Format for Each NMEA 0183 Port
You can configure the communication format for each internal NMEA 0183 port when connecting your chartplotter to external NMEA 0183 devices, a computer, or other Garmin devices.
Select Settings > Communications > NMEA 0183 Setup > Port Types.
Select an input or output port.
Select a format:
To support the input or output of standard NMEA 0183 data, DSC, and sonar NMEA input support for the DPT, MTW, and VHW sentences, select NMEA Std..
To support the input or output of standard NMEA 0183 data for most AIS receivers, select NMEA High Speed.
To support the input or output of Garmin proprietary data for interfacing with Garmin software, select Garmin

Repeat steps 2–3 to configure additional input or output ports.