USB charger hangs c550

This has been discussed on other forums... in the Garmin car charger, one of the pins in the USB cable is connected to ground through a resistor that is different from that found in a standard USB port. This results in a different voltage on that pin, so the GPS "knows" it is connected to a power source, and not to a computer, and it will then operate in its normal GPS mode. If the voltage on that pin is what a standard USB cable provides, then the GPS assumes you've connected it to a computer, and it sets itself to that mode. So there isn't anything wrong with the way your unit is working. If you're handy with electronics, you can modify a USB cable so the unit stays in GPS mode even if connected to a USB adaptor, or a USB connector on a computer. Here's a link to some information: http://pinouts.ru/GPS/garmin_nuvi_power_pinout.shtml

Thanks Dsorgnzd. Pin X is not connected in the Radio Shack ac type-A USB adapter, only pins 1 (5v) and 4 (GND). This does charge the unit, however, I think their pin X with 17K resistor is "Exclusive OR'd" inside the GPSr, so that when disconnected, it acts as a restart/reboot command. But should'nt the pin X to pin 4 termination be a function of the Garmin-provided USB cable?

Ah, but there isn't a standard for using USB as a battery charger, is there?

I believe that resistor is used to select the Fleet Management Interface. In Fleet Management Mode, the mini-USB connector, becomes a TTL-level RS232-C port. A side-effect is that it will now charge, without going into Mass-storage-mode.

Also, on the C5xx series, there are two different USB modes...if you hold the "Time" for 7 secs to go into Diagnostics mode and then connect the USB, it enters 'Garmin USB GPS' mode. (This is the mode that older units, like the C3xx series use by default). If you exit the diagnostics, you can continue to use it as GPS, but charging from the USB - or, you can press the Power off switch.

(And just for good measure, the C5xx has behaved differently with different firmware revisions...)

That's pretty handy to know. Wish I'd known that during my hotel stay in the Bahamas last week. Entering USB GPS mode from diagnostics mode would have saved time by plotting activities while charging at the same time. Is there some place to find out more of these useful little tid bits? Garmin's owner manual barely skims the surface on what the unit can do.

Interesting. My Nuvi 200 (which, as far as I know, has no "fleet management" mode) does the same thing. If I try to use it in the car, with the car charger that works with my Etrex Venture and my pda's (plugs into the cigarette lighter, and accepts a standard USB cable), the Nuvi goes into mass storage mode, just as if I had plugged it into a computer. I had hoped to avoid having to carry around another adapter in the car, but no such luck.

Lots of discussion on this topic of USB chargers and the problem of going into storage mode when charging. Bottom line - don't worry about it. It charges when in storage mode, too.

http://www.poi-factory.com/node/8313
http://www.poi-factory.com/node/9330
http://www.poi-factory.com/node/10701

This is great information. I'll be modifying some of my cables in this way so I can use them.

I wonder if such a cable will still charge my other USB devices? I should try to charge my hands-free headset, my Motorola Razor and my bluetooth GPS with the garmin cable and see if it still works for that.

Having just the one Garmin cable is becoming an issue with all the different vehicles I drive in a typical workweek.

Garmin, in forcing us to use their proprietary cable totally messes up the whole concept of standardization that USB is supposed to use to solve the complexity of different chargers for every device. There should be some sort of USB standard that certifies USB devices and does not allow any device that does not comply with this standard to use the term "USB" in their literature or marketing.

You'll probably find that the cables don't contain the conductor you need to connect to. (ie there's only 4 wires in there, not 5 (according to the USB spec)).

They're using the "ID" pin as a means of determining what type of device has been connected. The resistor denotes that it is a Garmin charger, capable of supplying up to 1A.

If they didn't use this method, consider what the USB 2.0 spec. says:

The power source and sink requirements of different device classes can be simplified with the introduction of the concept of a unit load. A unit load is defined to be 100 mA. The number of unit loads a device can draw is an absolute maximum, not an average over time. A device may be either low-power at one unit load or high-power, consuming up to five unit loads. All devices default to low-power. The transition to high-power is under software control. It is the responsibility of software to ensure adequate power is available before allowing devices to consume high-power.


I understand that to mean, that a device can safely only draw 100mA from a simple, non-intelligent charger. To draw any more, a software conversation would have to take place first. In other words, the generally agreed statement that you can always count on 500mA from a USB port just isn't true.

[This web-site http://www.usbmadesimple.co.uk/ums_2.htm seems to confirm that. See the section titled "Device Powering"]

[EDIT: [See also http://en.wikipedia.org/wiki/USB#Mini.2C_Micro
the section titled "Non-standard devices"]

The USB 2.0 spec. has moved:
http://www.usb.org/developers/docs/usb_20_040908.zip

(probably because there's now a USB 3.0 spec...)

It turns out that there is also a newer specification for USB Battery Charging, but I've not noticed any devices making use of it.
See http://www.usb.org/developers/devclass_docs/batt_charging_1_...

All in the name of progress.