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ContinuousWave: Small Boat Electrical
NMEA-0183 Serial Data Problem
|Author||Topic: NMEA-0183 Serial Data Problem|
posted 05-29-2011 09:39 AM ET (US)
My Standard Horizon GX1500S Class D VHF and Garmin 740S GPS are no longer communicating [via NMEA-0183 serial data connection]. The VHF is not receiving the GPS position information.
This is a new condition discovered after the boat was idle for several weeks and was towed about fifty miles last week.
I suspect the connections at the terminal strip may no longer be making good contact. A quick visual inspection did not show any looseness or corrosion.
Other than checking across the terminal strip for continuity I don't have a clue of what to do next. The next step will probably be to call SH and/or Garmin for additional guidance.
I also need to update the Garmin software though it is very unlikely to solve the problem as the system has been working perfectly for almost a year. The only other recent problem has been with the Garmin failing to display depth until it has been restarted, sometimes as often as three times. I hope the update at least cures the loss of depth information.
I'll report back when the malfunction is corrected. Meanwhile, if you have experienced this problem and can offer a solution I'd appreciate your input.
posted 05-29-2011 09:59 PM ET (US)
I would do three things.
First check the menus on both devices to ensure that no one messed with the nema settings for either the GPS or the radio. Be sure that the GPS is talking in the same format that the radio is listening.
Second check the grounds on both the radio and GPS.
Third check the connections going from the GPS to the radio again.
posted 05-29-2011 10:12 PM ET (US)
Your GPS would not turn on if it was not grounded. The 740 uses the power ground as the NMEA ground (there are no other NMEA grounds other than the power) ground. Check your terminal strip, then check your comm set up on the 740.
posted 05-30-2011 08:30 AM ET (US)
It is difficult to diagnose problems with serial data connections unless you have specialized test equipment. You can approach the problem at three levels:
--check the electrical connections to be certain they are still good; you will have to physically inspect each connection.
--check the serial communication port settings to be certain they are compatible; the baud rate must be set the same for both sender and listener;
--check the settings for the data that is to be sent across the connection; some DSC radios require specific sentences to be sent; be certain the GPS is sending the necessary sentence.
posted 05-30-2011 11:00 AM ET (US)
Thank you Tom, Jim and Fish. I will check the comm settings. I've never changed the settings since day one but I may have inadvertently done something while knob diking around.
The multiple reboots to get depth readings is a troubling problem. I hope the 740 is not going "tango uniform".
posted 06-01-2011 07:33 PM ET (US)
Two days ago I finally downloaded the software update, version 3.0, and this morning installed it in the 740. IMO, Garmin's software download page could be easier to use. I clicked on the 740/740S on the page so many time my mouse went on strike. Come to find out, finally, all I had to do was click on a big word that said Download. Apparently it downloads multiple updates for multiple units and the unit decides what it wants during the unit update. Anyway the update is installed.
I won't know if the sounder will now function properly until I get in the water. Any hints on how to check a sounder transducer out of the water?
The 0183 connection to the VHF continues to malfunction and I have not yet figured out how to check/set the baud rate to 4800. Guess I'll have to call Garmin again.
My brain is just too old for this stuff. I'd pay extra for idiot proof gear which I could not screw up.
posted 06-01-2011 07:47 PM ET (US)
Butch--Don't give up. It is not your fault that interconnecting marine electronic devices which employ the NMEA-0183 serial data protocol is difficult. The NMEA really dropped the ball on this standard. There are many varieties of color coded wiring used--every manufacturer seems to have his own standard. There are variations in input and output circuit design: some are differential and some are not. And there are confusing labels applied. If I did not have more than two decades of experience interconnecting devices from different manufacturers via serial data ports, I would be in the same quandary you are. It takes far more electronic and serial data communication knowledge than it should. That is not your fault, it is the National Marine Electronics Association's fault. They should have developed a better standard.
posted 06-01-2011 10:38 PM ET (US)
Hang on buddy .......
The FF part of your 740S will work just fine. Next time you turn your unit on you will see what software version your are running but if you miss that display that's OK. Here's how to see what software version your running. From the main menu screen press the Config Menu>System Menu> then you'll see this display. It has all sorts of data on it.
Now for the NMEA setting ... piece of cake ..... From the main menu display select the Config Menu it will open into this display.
From the above display select the Communications Menu and then you'll see this display.
From this display ensure Serial Port 1 & 2 both say NMEA Std. If they don't touch each serial port menu and change same if they are set correctly don't touch nothing. Everything else if fine.
As to the Garmin Update Web site they just went to this format at the request of the users. It's very simple to understand. Just click download and everything you'll need for your unit is there. By the way the latest update is V3.4.
Next NMEA wire connections.
The 740's power ground is also the NMEA ground. So if your 740 turns on you have a good NMEA ground. The SH 1500 uses the green wire as a ground so ensure it is connected to a common ground source. The SH 1500 Gray wire receives GPS info from the 740 so that is the one you should check.
Keep the faith my friend.
posted 06-02-2011 09:32 AM ET (US)
Jim & Tom,
You guys are terrific. Thanks for the morale boosting comments and the detailed how-to information. Hopefully I'll get on it again this afternoon.
posted 06-02-2011 09:35 AM ET (US)
Based on the images that Tom provided above, it appears that GARMIN uses the notation "NMEA Std." to mean a "standard" baud rate of 4,800-bps and the notation "NMEA HS" to mean a "high speed" baud rate of 38,400-bps for the NMEA serial port configuration. The 38,400-bps baud rate is generally used only when interfacing to automatic identification system (AIS) devices.
posted 06-02-2011 04:53 PM ET (US)
There are more parameters in a serial data connection, but, mercifully, GARMIN appears to leave those (properly) preset and not available for change. However, check the settings on the other device to make sure they are compatible with the "standard" used by GARMIN. The usual settings are
DATA BITS = 8
posted 06-07-2011 08:23 AM ET (US)
The Garmin 740 has NMEA 1083 Diagostic functionality built into the software. To get to it you from the Home screen you go to the Config Menu>Communications Menu>NMEA 0183 Setup menu>Diagnostics Menu.
Here's the dislay sequence .....
NMEA 0183 Setup Menu
Diagnostic Functionalities .... you have two ways to view NMEA 0183 input/output.
1. Using the display
2. Recording to an SD card ...1 gb will get your three hours of data. You display this data from the Notepad app.
There you go ....
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