GPS Baud rate?

Submitted: Sunday, Feb 13, 2005 at 14:24
ThreadID: 20399 Views:2501 Replies:5 FollowUps:1
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Just upgraded my laptop to a new 80GB hard drive and have reinstalled OziExporer and Magellan Map330 software as a result. Got it all working fine but I'm wondering if it is better to have a higher baud rate (whatever that is)? Does that mean it will run faster / better?

It has always worked fine at 4800, but both the GPS and laptop can go to much higher baud rates (9600, 19,200 etc). I've been experimenting and it works on these different settings, but is there a reason it is set at 4800? Unfortunately I can't drive at the moment so I am unable to do the obvious thing and test it out and waving my GPS around in the air has so far proved inconclusive.

Thanks
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Reply By: Member - Chrispy (NSW) - Sunday, Feb 13, 2005 at 14:41

Sunday, Feb 13, 2005 at 14:41
Serial (RS-232) devices usually start at the lowest usable baud rate in order to be able to assure that they will talk to each other. There are many variances on how fast you can push this connection - quality of cable, length of run, signal strength of both the DTE and DCE ends (data and carrier equipment), external RF interference, etc, etc, etc.

4800 bps is a nice slow standard to start with. The reason that your device starts there is because it will most probably work at that speed. If you try bumping your speeds up at either end (in unison of course) until you have problems, go back a notch - find a good medium and stick to it. I successfully run at 9600baud all of the time, and you really shouldn't need to go any faster to transmit/receive simple NMEA data such as waypoints and track logs. If you were downloading maps and such, then you may want to go for the highest speed you can - up to (probably in your case) 110kbps - which is fast as most UARTs (serial data communication chips) in laptops work.
AnswerID: 98134

Follow Up By: V8Diesel - Sunday, Feb 13, 2005 at 15:05

Sunday, Feb 13, 2005 at 15:05
Thanks for that mate. Got them both up to 19,200 but they are unproven, sounds like I'll drop it back a notch to 9,600 as suggested.
0
FollowupID: 356646

Reply By: Jarrod - Sunday, Feb 13, 2005 at 15:42

Sunday, Feb 13, 2005 at 15:42
V8Diesel, The NMEA string provided by your GPS only appears once every second. The Transmit time between your GPS and laptop is (at 9600bps) for a standard nmea string only about .2 of a second. For the other .8 of a second nothing is happening!! ( computer waiting for next gps string!) therefore, the standard settings are 9600 bits per second(baud rate), being a very reliable and robust speed. If you increase Baud rate, there are no advantages, as I mentioned earlier, nmea gps strings only appear every second....

Hope this helps...

Jarrod.
AnswerID: 98138

Reply By: Charlie - Sunday, Feb 13, 2005 at 19:37

Sunday, Feb 13, 2005 at 19:37
Never had any luck getting my Magellan to function higher than 4800 but if it works go for it ,can't do any harm.
Regards Charlie
AnswerID: 98171

Reply By: pjchris - Sunday, Feb 13, 2005 at 20:15

Sunday, Feb 13, 2005 at 20:15
Actually if you turn on all the possible NMEA strings (RMC,VTG,GSA,GSV,GGA and VTG) they comprise more than the 480 characters that 4800 baud can transmit in one second.

When you use moving map software the sooner the laptop gets the string from the GPS the sooner your position will update. While the difference is small it can be noticed.

I run my current GPS at 19,200, and the previous one (A Holux GM210) at 38,400 or 57,600 (both worked).

As has been said 4800 was the chosen standard and is enshrined in the NMEA standard. It will work with anything.

Some chipsets you cannot change the baud rate. I have had SirfStarII and SirfStar xtracII GPS and changed the baud rate but I could not get the Evermore chipset GPS to run at anything but 4800.

Peter
AnswerID: 98182

Reply By: Foss - Sunday, Feb 13, 2005 at 20:28

Sunday, Feb 13, 2005 at 20:28
G'day V*Diesel

It's simple really. If your GPS & PC can be set at identical baud rates they will be able to communicate using RS232. I had a garmin 12xl that ran fine at 9600. I now have a GPSmap76, kind regards to the thief that stole the old one, and it doesn't allow anything other than 4800 in NMEA mode as far as I can tell.

cheers

AnswerID: 98189

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