Problems Connecting to a GPS

 

iPaq handhelds:

When using an iPaq handheld make certain that the "Use RX_FLAG" option on NMEA setup is not checked. iPaq serial port driver does not send required notifications. 

Simulator mode:

It is tempting to hook up a GPS unit to your computer, turn it on to a "Simulator" or "Demo" mode and  play with it. It works fine with some GPS units like Garmin 12XL. However, some (I believe Lowrance Airmap 100 is one 

of them) output NMEA sentences which are stamped as invalid when set to simulator mode. GPS_LOG WinCE ignores such sentences, and thus it will seem that things do not work. Take the system outside, and try on real GPS data.

"No GPS" indicator:

You may connect your GPS correctly and still get the "No GPS" indicator button indicating no data coming it. This is probably because you are testing indoors (Navman GPS exhibits this behaviour). Just as in the simulator mode, data are sent, but are marked invalid. To test for data connection to the GPS enable raw data logging in the logging tab of settings. That will create a rawGPS_LOGdata##!!.txt file which will contain everything that comes in on the serial port. This file needs to be manually deleted, any new data will be appended. Raw data logging setting is not remembered between different program sessions. If you are receiving data and are testing outdoors, and still get the No GPS indicator, e-mail me the raw data log file and I'll take a look at it.

Cable:

There seems to be a general misconception that all one needs to do is to connect two cables together, and everything should work. When it comes to RS232 cables that is not quite true. For the most part the cables conform to a de-facto standard shown below ("modem" in this case means anything that is not a computer)

Note that as you connect a modem to computer a receive signal pin matches up with transmit signal pin. Unfortunately, a typical RS232 cable supplied with a handheld Windows CE computer is expected to be plugged into a PC, thus makes the handheld to look like a modem. Of course the same is true for a GPS unit. In order to make it work you need an intermediate "null cable" that switches pins 2 and 3.

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