Frequently Asked Questions (FAQ) on the Garmin Protocol

Master FAQ Index

Other Garmin / VirtualPC Notes

These User Notes follow the FAQ entry on using VirtualPC to flash the ROM or upload maps to Garmin GPS units. Please note that we have quoted the users verbatim (with their permission) and that Global Mapping Systems cannot vouch for the accuracy of any of this information. As with the other FAQs, please under we are presenting this information "as is" with no implied warrantee.

Please with your commends and feedback, we'd love to hear how people are doing and add to the notes below.

Date: Wed, 19 May 1999 23:17:15 -0700
From: Tom Harvey 
To: Karen Nakamura 
Subject: More info for your VPC-Garmin FAQ

I installed my upgrade daughter board to upgrade my PB 1400c/117 to a Nupowr 
G3-250 with 1MB L2 cache, and have now uploaded maps to my GPSIII+.  Here are
some of my observations.

1)A single map of 127 KB would not load at Auto or 115,200 data rate settings.

2) At the 57,600 rate I was able to upload the same 127KB map or a 2 map set
of 447KB, or a 5 map set of 1302 KB.  No failure at this setting.

3)  [problem with "upload to map" icon fixed w/ MapSource 2.01 update on 
	Garmin support web site.
     entry removed at request of author 99/5/20]

4) I had correspondence with a person with a 604e/240 who was having trouble
uploading at 9600, so I related to him the following experience I had on the
slow Pentium:  the upload failed at 38,400, but worked at 57,600.  The Mac guy
then wrote back that he then tried other com rates, and that 57,600 and 38,400 worked.

5)  Another interesting observation from the slow Pentium experience that
might also apply to VPC is that at 38,400 we could upload a single map, but a
set containing multiple maps failed at that rate.

6)  You were surprised that my software upgrade with the 117 MHz processor
worked.  Here is a little more detail on that.  The screen said that the rate
was either 562 or 652, I can't remember which, the rate was the same during
the whole process, and the upload took about 17 minutes.   As to why the
upload of maps seems to be sensitive to processor speed/data transfer speed
and the firmware upgrade is not, I really do not know.  I guess it could be
due to something on the GPS end or the computer end and most of the comments
I have seen from knowledgeable people seem to suggest the GPS end, but could
it be this:  the firmware upgrade is a more uniform transmission, but there is
something different about the map data that can make the data rate change.  In
other words could there be something about the map data that makes the
transfer rate from the processor to the com port vary?  I have heard people
mention that they have had map uploads fail at various points in the process
and that would seem to be in line with the hypothesis of changing data rates
depending the uniformity of the map data processing.  So if the GPS is
expecting to see data coming at a certain rate, and the rate then changes it
chokes (or "times out" as one person on the internet has put it).  (By the way 
I know this could be a bunch of hot air --- communications is one of the most 
mysterious things about computers to me.)

7) I have a minimal amount of software on VPC.  Windows 95, was installed
minimally (no Internet Explorer for instance).  About all I am aware of is
Mapsource and some text software on the C drive and g7to (DOS version) on the
shared folder F drive.

If you read all that, congrats, I did get a little detailed :-).
Tom Harvey

Date: Fri, 05 May 2000 19:18:45 -0400
Subject:  Comments re VirtualPC/Windows98 & Flash Upgrade
From: "Robert T. Joyce" 

I just completed a ROM upgrade in my Garmin 12MAP, from version 2.01 to
Verson 2.03, using Connectix's VirtualPC 3.0.3/Windows98 on a G3/300/96 Mac
(Beige).  It went very smoothly, taking only 2-3 minutes to complete .  The
suggestions found on the GPSy web site were quite helpful.

My procedure:

Install new batteries in the 12MAP.  Connect the 12MAP to the Mac serial
printer port (I use an ABCD serial switchbox for this connection).  Turn the
12MAP on, turn Simulator on, go to the Set-Up/Interface menu and set Format
to Garmin and Transfer Mode to Host.

Start the computer 

In the Control Panel,
o  Disable Virtual Memory, Energy Saver, and all screen savers
o  Turn off AppleTalk

Restart the computer

o  Open VirtualPC (with recommended memory partition)
o  Under Edit/Preferences, ensure that COM2 is the printer port
o  Set COM preferences to Non-Modem Device
o  Drag-copy Garmin updater from Mac desktop to Windows desktop
o  Double-click the .exe file, un-zipping it to C:\Garmin
o  Run the updater, letting it automatically find COM2 for the 12MAP
connection and automatically select the transfer rate (in this case

It took about 30 seconds for the updater to erase the ROM, and maybe two
minutes for the program to write the new firmware to it.

All very uneventful, but GPSy's warning that a power failure during this
process could disable your GPS unit is TRUE; without an uninterruptable
power supply on my compter, I held my breath for the time it took to
complete the ROM upgrade.

After upgrading MapSource U.S. Roads and Recreation from version 3.0.2 to
version 3.0.3a, I successfully downloaded about 1.2 MB of maps (8 counties,
in this case) to the 12MAP.  That required about 3 minutes.

The usual disclaimers about liability apply to my comments, of course.

Date: Wed, 19 May 1999 
From: Michael Haensch 
To: Karen Nakamura 
Subject:  Garmin III+ and Apple/Mac


On a PowerMacintosh 9500 with a UMAX 250 MHz 604e processor card, 160 MB
RAM and a 8.1 GB IBM DDRS UW linked to a Formac PowerRaid I (any
"Fast-SCSI" HD should do the trick), I could successfully upgrade the
software of my GARMIN GPS 12 v4.0.2 to v4.5.4 multilingual. This will
not work for every GPS 12 source ROM version (i. e. not below 4.0).
Check with Garmin or your local distributor.

I took my selfsoldered standard Garmin/Mini-DIN-8 cable, -which is known
for working with GPSy- and started a freshly installed unmodified
Connectix Virtual PC 2.1.2 (80 MB memory partition) on MacOS 8.5.1 US.
The trick should work with MacOS 8.6, for which Virtual PC 2.1.3 update
is essential. 

A nice ability of Virtual PC is the transfer of files from the Mac- to
the WIN-Desktop with a simple drag & drop. In Windows 95 I started the
GARMIN update program, which automatically identified the GPS receiver
(I defined the Mac printer port as the only port available - COM2) and
started the update, which was quite slow with approx. 800 - 900
bytes/sec, but successful after around 7 minutes. Dont work at anything
else in the background! 

You should use a CLEAN 8.5.1 system, and make sure to disable "Energy
saver" control panel settings - no background process should disturb
Virtual PC. No serial port enhancers like "serial speed 230" or similiar
shoul be present & loaded. You MUST update Virtual PC to version 2.1.2
on MacOS 8.5.1. Make shure choosing the GRMN/GRMN protocol on the

Faster machines (like grey G3 Macs except the Yosemite w/o serial ports)
should make it even better. This procedure DOES NOT work with Insignia
SoftWindows 5.0.5 95/98.

Michael Haensch

DISCLAIMER: I am _NOT_ liable to any damage you add to your GPS receiver
acting upon my experiences.

Date: Sep 9, 1999
From: Dennis Fraser 
Organization: LaserType MultiMedia
Subject: GIII+ 2.03 Updater & Mac

A note for those of us attempting to survive Garmin's rediculous,
narrow-minded, penurious policy of not providing Macintosh-compatible
software ...

I have quite successfully used all of Garmin's installers and MapSource
applications on my PowerMac 8100 (with Newer G3 upgrade) using VirtualPC
emulation software. Successful that is until the advent of Garmin's new
Windows-based updater (GIII+ 2.03). This new installer would communicate
with the GIII+ long enough to erase the old software, but stall at 1%
into uploading the new. This problem was evident regardless of comm port
speed or disabling high-speed transfers in the Garmin software. 

After many hours of testing, it was discovered the Newer G3 extension
itself was effecting the comm/printer port in a manner Garmin's
application didn't favor (or possess appropriate error trapping to
overcome given there is no such error with the earlier updaters and/or
MapSource PC software). Removing the Newer G3 extension (as well as the
expected  modem software, Open Transport, etc.) allowed the Garmin app
to run in a proper manner. Further testing reveals the same
problem/solution is effective for the Garmin database updater for the
GIII-Pilot software.

Perhaps this observation will save someone else the grief encountered
thanks to Garmin's policy to benefit only the poverty-stricken Bill



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This page was last updated on June 19th, 2000. We've had [N/A] hits since May 20, 1999.