[aprssig] APRS and Garmin Nuvi

Scott Miller scott at opentrac.org
Fri Feb 1 16:17:13 CST 2008

Yeah, my Garmin rep confirmed that it's just a level converter, 
resistor, and ESD protection.  Even my dealer price (at < 10,000 unit 
quantities) is rather obscene, though.

Sounds like it uses the undefined extra pin in the mini-B connector, 
which means I've got to hunt down a source of a 5-conductor USB cable to 
do some prototyping.


Alex Carver wrote:
>> Date: Fri, 01 Feb 2008 07:45:55 -0800
>> From: Scott Miller 
>> Subject: Re: [aprssig] APRS and Garmin Nuvi
>> Looks like a standard mini-B to me.  That's not to
>> say they couldn't 
>> overload the pin functions - you can already signal
>> things like bus 
>> resets with single-ended conditions on the
>> differential lines.  Could be 
>> as simple as a pull-down on the + line that switches
>> D- and D+ to RS-232 
>> operation.
>> The blob on the cable isn't large enough for
>> anything bigger than an 
>> LQFP32 at most.  I really don't expect to find
>> anything that complicated 
>> in there.
> There's probably nothing more than a resistor or two
> in the cable.  This is a pretty common thing to do
> with dual protocol devices.  Think back a bit to
> standard keyboards.  A bunch of the USB keyboards also
> came with the PS/2 adapters (and some mice, too).  The
> USB client chip on board could look at the signals and
> loads present on the pins and determine which type of
> port it was connected to and then speak that protocol.
>  The pins there were overloaded as well.  Same thing
> here.
> With USB-To-Go still a bit of a ways out, RS232 is
> still the nearly universal, easy way of getting things
> to talk together.  So this is the nice, cheap way of
> getting the benefits of both into one package with one
> chip.  You can talk to it by USB or you can still talk
> to it by RS232 (probably with some limitations) and
> satisfy multiple customer markets with one reference
> design and a few extra lines of code.
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