GPS strings.....

[wannaBinventor]

I'm writing a GPS program right now but I want to fully understand something first.

NMEA strings are sent out from what I understand once every second. Say it puts out the following sentences (all at 4800 baud):
GGA, GSA, GSV, RMC, VTG, GLL

I'm trying to understand when those sentences get sent out? Does the 1 PPS second normally correspond to the beginning of the sentences? Are they normally sent out in the order that they are listed in the datasheet?

the UART will be interrupt driven, so I guess it really doesn't matter, but I'd like to know. Datasheets and tutorials seem to only want to tell you that it's sent over UART and what the sentences are.

 

[MikeMl]

The period between say GGA sentences varies depending on the length and number of other sentences. If you can configure the sender to eliminate some sentences, then the rate of getting the one(s) you want will increase.

 

[DirtyLude]

^ That doesn't happen with the one I use. I only have experience with the Venus module, but the default update rate is 1 Hz, so string sets are sent out at 1 second intervals no matter what you have selected to return. You can increase the update rate to 2, 4, 8... Hz, but you need to increase the bitrate at some point to keep up with the datastream.

I have no idea what the order of strings is, or if there is even set order. If you can hook yours up to a serial connection on your PC and dump the data to a terminal, you can check it out.

 

[MikeMl]

I use Garmin GPSs. They are configurable. At 4800 baud, the time to send the sentences exceeds one sec.