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How to initialize GPS?

 
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oxxyfx



Joined: 24 May 2007
Posts: 97

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How to initialize GPS?
PostPosted: Thu May 06, 2010 1:44 pm     Reply with quote
Hello,

I am trying to send a string to the GPS module connected to the UART of the 18F2550.

UART interrupt for receiving works fine, I can display the incoming data on the LCD connected to the same PIC.

What I am trying to do is to send a $PMTK string to the GPS to send me only the relevant GGA and RMC strings only.

I tried this:
Code:

void initgps(){
   disable_interrupts(INT_RDA);
   delay_ms(100);
   printf("$PMTK314,0,1,0,1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,*28");
   delay_ms(100);
   enable_interrupts(INT_RDA);
}

but I am not getting the desired effect, all other NMEA strings still coming in.

What am I dong wrong?

Thank you.
PCM programmer



Joined: 06 Sep 2003
Posts: 21708

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PostPosted: Thu May 06, 2010 1:50 pm     Reply with quote
All NMEA sentences are supposed to end with a CRLF pair (0x0D, 0x0A).
In a CCS printf statement, it would be this sequence: "\r\n"
oxxyfx



Joined: 24 May 2007
Posts: 97

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PostPosted: Thu May 06, 2010 2:42 pm     Reply with quote
Thank you,

so that woud be the following:

Code:

void initgps(){
   disable_interrupts(INT_RDA);
   delay_ms(100);
   printf("$PMTK314,0,1,0,1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,*28\r\n");
   delay_ms(100);
   enable_interrupts(INT_RDA);
}
Ttelmah



Joined: 11 Mar 2010
Posts: 19498

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PostPosted: Fri May 07, 2010 3:51 am     Reply with quote
Except, 'why disable INT_RDA'?.
The modem _will_ send a reply. This needs to be at the very least removed from the hardware serial buffer. Even if 'errors' is selected, which will prevent the UART from becoming 'hung' because of the unhandled reply, there will still be two characters waiting to be read.
Leave the interrupt enabled, and then have a simple routine to empty the serial buffer, assuming you don't actually want to check the characters returned.

So (assuming a serial routine like EX_SISR), something like:
Code:

void initgps(){
   delay_ms(100);
   printf("$PMTK314,0,1,0,1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,*28\r\n");
   delay_ms(100);
   while (bkbhit) bgetc(); //Throw away reply.
}


Best Wishes
Jiewy



Joined: 27 Apr 2010
Posts: 8
Location: Penang Malaysia

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PostPosted: Wed May 12, 2010 3:40 am     Reply with quote
Hie there, i am trying to receive nmea data through uart to make sure that i am receiving it properly before parsing it. But so far, no luck. Can u pls share ur experience with me?

This is my coding but i am not sure if its correct.

Because when i applied it to the hardware, when i start up, my lcd gives me giberish straight away and when i on the gps, the giberish changes but still giberish. Can u pls help me in this matter?
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