Frequently Asked Questions (FAQ) on the Garmin Protocol

Master FAQ Index

Does GPSy support the new map upload CD-ROM features of the Garmin GPS III+?

New Garmin GPS III+ receivers have come out in the 1Q1999. These new units are unique in that they have flash EPROM in them that allows the user to upload fine detail maps of their county, state, or country using Garmin's MapSource CD-ROM program.

Unfortunately, Garmin has apparently made the decision not to license the details of the map uploading protocol or the format of the MapSource CD-ROMs to any third-party. This means that it is unlikely that you will see any third-party programs on either the PC or Mac support the map upload protocol.

What this means for Mac users is that no Mac program will be able to natively upload maps to the Garmin GPS III+ or any future models that use this method. You will need to use a PC emulator such as VirtualPC or SoftWindows to emulate the Garmin MapSource CD-ROM program.

Garmin also apparently holds the same policy in regards to its FLASH EPROM firmware upgrades for the rest of its units. This means that if you wish to FLASH upgrade your Garmin handheld to a later software revision, you must use the Garmin PC program under emulation. We recommend that if you have a slow machine (non-G3), that you don't try the FLASH upgrade under emulation as any glitch in communications due to slow emulation can result in an incomplete transfer and you will need to send your Garmin in for repair.

Global Mapping Systems (us) of course regrets that Garmin has made this direction in policy. We would like to suggest that customers who are affected by this policy write to Garmin and suggest that Garmin license these two key protocols to third-party vendors. We have offered this to Garmin in the past, however they have not replied to our inquiries. Although we give the e-mail address, we'd strongly suggest writing real letters as they have more impact. Address them to the President of Garmin International, Gary Burrell.

		Gary Burrell
		GARMIN International Inc.
		1200 E. 151st Street
		Olathe, KS 66062 (Kansas City metro area)
		Phone: (913) 397-8200
		FAX: (913) 397-8282

Why can't GPSy auto-switch my Garmin from NMEA mode to Garmin data transfer mode automatically?

Unfortunately, neither the Garmin data protocol nor the NMEA protocol allow for such mode switching. We agree life would be much easier if it were possible since the NMEA protocol has so much more data than the GRMN protocol when in real-time mode. Write Garmin a postcard and ask them to add this feature!

The Garmin Real-Time Protocol seems unstable or slow

The Garmin protocol wasn't designed for real-time navigation purposes. Furthermore, since the protocol is bi-directional in nature rather than a streaming format like NMEA-0183, the synchronization between GPSy (the host) and the GPS unit client can get confused.

Because of this, the Garmin protocol has a tendency to "stick" or "slow-down" when put into real-time navigation mode. In addition, the Garmin protocol does not provide all of the datum and navigation information provided by the feature rich NMEA-0183 protocol. This means that you will not get the satellite position display or all the navigation displays possible with NMEA-0183.

Global Mapping Systems does not recommend full-time use of the Garmin real-time protocol for navigation purposes. We recommend use of the NMEA-0183 format instead. Note that newer Garmin units have a real-time "PVT" mode (noticeable by the PVT packets in the GPS Data Monitor in GPSy) that makes real-time mode considerably more stable, although it still doesn't provide satellite tracking data and may still slow your machine down.

Why can't I use download with the User Configuration or All Data commands on my Garmin?

Garmin has implemetented variations of its Garmin/Garmin protocol in its handheld GPS units. Due to ROM space limitations, some GPS units support some of the extended protocol formats (USER/ALL/PROX transfers); and some do not.

Garmin has even been known to not support these commands in the first release of a unit; begin supporting them in a following release; and then remove then in the third ROM revisions. We suspect that this has to do with saving ROM space.

There is no way to test whether your unit supports the commands other than trying them out. Garmin has not released a database of which units support which commands (which would have been complex, anyway, due to the above phenomena).

The simple answer is: If your unit supports the commands, it supports them. If not, it does not.

USER: The unit outputs its current user-settings (time zone, brightness, contrast, key beeps, etc.). The format of USER data varies from model to model, so you can only upload USER data to the same type of unit that downloaded it. Useful if you're conducting a hard reset of your GPS unit.

ALL: Downloads all stored data including waypoints, routes, track, and USER data. This command was only supported on a few units, it allows for quick backup and restoration of a GPS unit.

PROX: Proximity waypoints. Only Garmin handhelds with proximity waypoints support proximity downloads. See the manual for information on what a proximity waypoint is.

When I upload data, my Garmin reports Data Transferred before all of the data has been transferred

Before uploading data, GPSy queries the Garmin GPS-unit on its feature database. These queries cause the Garmin to report "Data Transferred" -- meaning that the data query has been acknowledged -- before the main data transfer has even begun.

Whether one considers this to be a bug, feature, or something to worry about at the same level as global warming and mad cow disease depends on whether you are a software engineer or hardware engineer.

How can I use VirtualPC / SoftWindows to upload MapSource maps or flash the firmware on my Garmin?

Recent Garmin GPS units support uploadable maps or flash upgradable firmware. Unfortunately, Garmin has not released Mac versions of their map/flash software; have not announced any plans to do so (or even contemplate the issue); and have refused to license the protocols needed to interested third-parties (such as ourselves), even with the offer of royalty fees. Sigh.

Fortunately, if you have a relative fast Macintosh PowerPC, you can use VirtualPC or SoftWindows to emulate a PC and use Garmin's own native software under MS-DOS or Windows. Ugly, but an option. We strongly suggest using a real serial port or serial PCI card (such as the Megawolf Romulus or Orange Micro Grappler) rather than a USB serial port, the USB drivers just can't seem to keep up with high-speed protocol transfers.

To sucessfully transfer data, you need a fast PowerPC since Intel/PC serial ports aren't well designed and the emulator struggles with them. We recommend a 250mhz or above PowerPC 603 , but people have managed with slower machines. See the separate User Notes for details. E-mail us with your own results and we'll add them to the list.

Here are some configuration tips:

  1. On the new 3V Garmins (eMap, eTrex) INSTALL NEW ALKALINE BATTERIES. This cannot be emphasized enough. These units can't supply enough voltage to the serial ports if they are running mid to low, or if they are running on NiCad/NiMH batteries which don't supply a high enough voltage.
  2. A solid serial connection is essential. Use the demo version of GPSy to make sure that bidirectional serial communication works. See our FAQ on serial problems and our page on data cables.
  3. Make sure your COM preferences in VPC are set to "Non-Modem Device."
  4. Set the serial port speed configuration in the Garmin program to "38400" (if Auto doesn't work)
  5. Turn off AppleTalk and VM
  6. Give VPC as much memory as you can (GetInfo:Memory)
  7. Quit all other applications, especially Internet Explorer (it hogs cycles)
  8. Quit the finder, if you have a finder quitting utility
  9. If flashing the ROM, be sure to boot in MS-DOS mode -- DO NOT USE MS-DOS MODE UNDER WINDOWS!
    We recommend Windows 95 for the MapSource program. Win95 is lighter and faster than Win98 or WinNT, the other two options.
  10. Turn the unit to GRMN/GRMN mode; turn Simulator mode on (lessens the CPU burden on the GPS unit)

If you still have problems, see the User Notes from other users.

Note: We do not recommend flashing the ROM (upgrading the firmware) on anything less than a G3. While a communications failure in the MapSource uploads is relatively harmless (a corrupted map database can be reinitialized); a failed firmware upgrade will render your Garmin unit absolutely useless -- your only option will be to send it into Garmin for repairs.

This information is provide "as-is" as a service to our customers. You assume all liability for using it. If you are nervous about this in any way (and you should be; if you're trying to flash your ROM under emulation); DO NOT DO IT. Borrow a friend's PC and do it there.

Some users have also written back with feedback and comments on how they've managed to get VirtualPC running. It's quite informative, so please see: Garmin Virtual/PC User Notes on Map Uploading and Flash Rom Upgrades


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This page was last updated on June 19, 2000. We've had [N/A] hits since March 2nd, 1998.