How to listen and decode multiple GPS sentences ?

Development Boards MicroMod
1

How can I do to listen to $GPRMC, $GPGSA, $GPGSV at sime time ? I can handle one, but 3 I don’t figure how to…

I have been using the Input S statement to wait for the sentence to come, validate and decode it.

Question is how to receive the 3 sentences and parse it without lose data ?

Looks my code only can handle one sentence (Main loop) using BascomAvr and a MT-128 module :

Thanks in advance : )

Input #2 , S , Noecho

For I = 1 To Len(s)

Q = Mid(s , I , 1)

Letra = Asc(q)

If Q = “,” Then

Commas = Commas + 1

End If

If Q <> “,” Then

If Letra <> 10 Then

If Letra <> 13 Then

Select Case Commas

Case 1 : _header = _header + Q

Case 2 : _time = _time + Q

Case 3 : _fix = _fix + Q

Case 10 : _date = _date + Q

End Select

End If

End If

End If

Next I

2

you need to capture all the output sentenses the GPS module spits out, then ones it has done that you parse through the data to get the fields you want.

3

I figure that. I was losing data but now I’m using buffered serial input and being able to listen to every sentence and have time to parse it. I’m running 2 sentences at 5hz rate : )

4

but now I’m using buffered serial input

Are you doing this in software or did you get a chip to do the work?
5

Franklin97355,

I’m doing it in software. By now it’s enough for me as the buffered mode for serial uses interrupts and take care of catch the 2 Nmea sentences each 200 milleseconds.

As a info,

Each time I power up the GPS I initialize it by changing the next modes:

from 4,800 to 38,400 baud

from 6 Nmea sentences to only RMC and GGA

from 1 Hz to 5Hz

I know that I can use a battery to keep the settings on GPS, or better yet to write permanently the settings in the GPS (allows for 8 permanent write down) but until the finall version I’ll keep working this way.

I’m using BascomAvr. Configure the serial port as need and then add the next:

Config Serialin1 = Buffered , Size = 150      'I named it "Serialin1"
Enable Interrupts

then listen for the input as usual:

Do 
   Input #2 , S , Noecho  
   _header = Gettoken(s , 44 , 1)  '<--- from Franz Josef Vögel library 
  
   Ss = Right(_header , 6)    'To remove the #10 from the first token only.. 

  Select Case Ss 
   Case "$GPRMC" :  Call Gprmc 
   Case "$GPGGA" :  Call Gpgga 
  End Select 
Loop

The interrupt service will work for you so don’t have to worry and concentrate in doing your math.