Forcing the etrex to accept a firmware

Use at your own risk - this tip may be helpful in getting the golf/euro etc. versions of the etrex to accept a US firmware, or one of the unofficial mountain-bike/ hikers versions. It is also useful for situations where the installed firmware is corrupted.  I have not tried this one, use at your own risk:

1. Make sure the etrex is loaded with fresh batteries or connected to a power supply, so it won't turn off in the following process due to low batteries.

2. Turn the etrex off.

3. Get the updated/modified firmware and run the updater.exe program

4. Set the correct COM port on the updater dialog box, but do not press OK on the screen yet.

5. Hold down the UP key on the etrex.

6. Turn the etrex on, while UP key pressed.

7. Press the OK button on the updater program and keep pressing the UP key until "SOFTWARE LOADING" or "SW LOADING" appears on the screen
   
   This will force the GPS to accept the updated firmware, no checks performed.
   

Other undocumented key sequences

The issue of the miscalibration was discussed with Garmin and they clarified the reset issue:

"The only issue at stake is the ability of the unit to lock on to satellites and calculate a position.

As we know from GPS 101, A GPS receiver must be precisely synchronized with the satellites to operate. We must know the exact time the signal left the satellite, and the time the signal arrived at the receiver, to calculate the time difference and corresponding range to the satellite. By knowing the precise location of the satellite when the signal left, and the range (pseudorange), we know our exact distance from that satellite (at that point in time). By performing this calculation on multiple satellites, we can triangulate and calculate our position.

Obviously, timimg is everything. We must have a precise timing source for this to work. We could install a rubidium or cesium beam oscillator in our GPS receivers, but this would be a little pricey, use a lot more battery power, and the unit would be a little bulky. Instead, we use a relatively cheap oscillator, and a lot of software finesse. Oscillator compensation data is stored in the unit as a table based upon temperature. When the unit locks on, it calculates the unit's oscillator error and enters a correction factor into this table based upon current internal temperature. In this fashion the unit is CONSTANTLY "learning" and fine tuning itself. We burn these units in when new to calculate and store calibration constants across the entire rated temperature range of the product.

What Darrin and the previous Email tried to explain, perhaps in different tones, was that running the GPS 12XL, or other GARMIN units, in test mode, would mis-calibrate the units internal oscillator if the unit locked onto the same satellite it expects to see in the factory environment when connected to a signal generator. The amount of mis-calibration depends on where this particular satellite happens to be in the sky. If the satellite is low on the horizon and heading directly towards or away from you, there will be significant doppler shift on the signal which in turn will grossly mis-calibrate our oscillator. This would be worst-case and statistically rare.

The net effect of this type of mis-calibration may range from long acquisition times to, on rare circumstances, failure to acquire at all.

If the latter occurs, as Darrin pointed out, the user can put the unit into Autolocate mode, which ignores oscillator calibration and the unit will lock on and begin to repair the correction table for each temperature it experiences. Of course, some users might not know to put the unit into Autolocate mode, they may see the unit not locking onto satellites and believe it to be malfunctioning.

As soon as the unit locks on, oscillator calibration is performed and peak accuracy is immediately restored. Of course, for complete repair, the unit will need to be locked on to real satellites for each temperature point that the unit was mis- calibrated to.

Darrin and I do not disagree on any points. He was stating his perspecive from a designers point of view, and I am giving you mine from the standpoint that we don't want anyone to erase the calibration from his unit.

GARMIN International 1200 E. 151st Street Olathe, KS 66062 USA"