I've been trying, off and on, to connect my Garmin GPSIII or Garmin GPSMAP 60C to my HP iPAQ 5555 PocketPC. I have the correct cable for the iPAQ (it's the sync cable, with an iPAQ connector on one end, and USB and serial (DB9) connectors on the other. The cable for the Garmin is the usual serial cable (it comes in at least two flavors: one with an automobile power connection, and one without).
Also needed is a DB9 - DB9 null modem, and a M-M gender changer.
Well, I could never make the thing work. Yesterday, I bought a new Kenwood TH-D7A(G) 144/440 MHz FM Dual Bander radio, which I'm going to use to experiment with packet radio and APRS (more on APRS to follow, time permitting). The radio purchase brought the whole Garmin - iPAQ problem up again. The Garmin gets connected to the radio, and the radio can be connected to the iPAQ. Since I couldn't connect the Garmin to the iPAQ, I suspected I also couldn't connect the radio to the iPAQ. Not good.
Well, I did a Google(tm) search on the news groups, and lo and behold, got a great hint. I have drivers installed for two kinds of keyboard: the folding type and the micro type (the type that slides on the bottom of the iPAQ and lets you type via a small keyboard). One of these keyboard drivers can be enabled at a time. Guess which COM port the keyboard driver snags? COM1. That's the port that the Garmin was busy sending its data to.
So, the trick was to go in to both keyboard drivers and ensure they were deactivated. Once that was done, the Garmin -to- iPAQ connection worked just fine. Turning the iPAQ off, then on again, yields a system hang which must be reset via a soft reset. It looks like if I reenable the micro keyboard before turning the iPAQ off, that problem is avoided.