Fieldpoint <-> Garmin GPS 25-HVS

[TheNet]

Here's a "simple" problem I hope you can help me solve.
I have a FP-2020 communicating with a Garmin GPS 25-HVS through its serial
interface, using LabVIEW 6.1 as programming language.
Specifically, I use pins 2,3,5 of the serial interface on FP as RX of NMEA
sentences coming from GPS, TX from FP to GPS for configuration purposes, and
GND respectively.
On GPS side, NMEA output pin (#12) is connected to pin #2 on FP's serial,
GND is the same as FP serial's, while pin #5 is connected to pin #3 on
serial port. The following scheme should clarify:

FP's serial GPS 25-HVS
pin 2 <----------------- 12 (NMEA output)
3 -----------------> 5
5 <------------------> 8 (GND, got from power line)

I can c
orrectly parse NMEA sentences pouring out of the GPS device's pin 12,
but problems arise when I try to write sentences from FP to GPS (i.e., to
write commands or request specific outputs from the GPS).Serial
communication is performed through FP real time serial .vi's

Since I don't see any answer to my requests I guess one of the following
happens:
1) I'm using a wrong write procedure
2) Electrical levels from FP serial port are not compatible with levels
required by GPS
3) Something more elusive is happening that I cannot spot...

I'd be very happy to attach my .vi and subvi to whomever is willing to help
me or is simply curious 🙂

Thanks to veryone
Nicola

[Mike S. @NI]

Nicola,

1. You can elimintate this possibility by using a simple command. Most serial devices have a very basic command that can be used to test communication. For GPIB, it is "*idn?"
2. This is unlikely, since the electrical levels used by the FieldPoint com port are the same as those by your PC. I have not used a Garmin device, but your wiring seems logical. Garmin should be able to provide the specs for the port or a standard that it meets.
3. If possible, I would recommend testing this with a PC or laptop. That way you could determine the problem lies with your cFP-2020 com port.

Regards,
Michael Shasteen
Applications Engineering
National Instruments
www.ni.com/ask
1-866-ASK-MY-NI