Miran,
If you are seeing the “Unable to Connect GPS” then this is not an issue with the NMEA data, it is an issue with attempting to open a file handle with the GPS. We use the CreateFile() function to open the GPS with a fileName of “COM#” where # is the COM port number you provided. Can you think of a reason why the GPS would be unable to open this way? Is it being interfaced in another application?
To answer your question, we only look at the RMC, GSV, and GGA sentences, but we only require the RMC to be present, if the others aren’t present then we ignore those values, but these sentences are only going to be looked at if the GPS is successfully connected, which it doesn’t sound like it is.
Regards