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ryan.reeve
Joined: 23 Jul 2006
Posts: 20
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| serial interrupt with GPS |
 Posted: Mon Nov 27, 2006 12:54 pm |
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Hi
I have connected GPS with PIC but all I receive are junk characters. Here is the code. Any ideas ?
| Code: |
#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#define SIZE 80
#define CR 0x0d
#define COMMA 0x2C
#use rs232(baud=4800, xmit=PIN_C6,rcv=PIN_C7, stream=GPS,ERRORS)
void parse();
void rmc();
void gga();
unsigned int j,k;
unsigned char *pChar,LastComaPos;
unsigned char inStr[SIZE] ;
unsigned char c;
int8 index=0;
#INT_RDA
void gps_isr(void)
{
c =fgetc(GPS);
fprintf(GPS);
c = (char)c;
if(c=='$')
printf(lcd_putc,"\%c",c);
index=0;
inStr[index]=c;
index++;
if((c==10)||(c==13))
{
inStr[index]='\0';
index=0;
}
}
void main()
{
lcd_init();
enable_interrupts(INT_RDA);
enable_interrupts(GLOBAL);
WHILE(TRUE)
{
parse();
}
}
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Last edited by ryan.reeve on Tue Nov 28, 2006 12:44 am; edited 1 time in total |
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drolleman
Guest
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| Posted: Mon Nov 27, 2006 1:02 pm |
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| where is your #use statement and clock? |
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drolleman
Guest
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| Posted: Mon Nov 27, 2006 1:07 pm |
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you need #fuses statement
#include <18f252.h>
#device ADC=10
#device *=16
#fuses H4,wdt128,NOPROTECT,NOBROWNOUT,noPUT,NOLVP,debug
#use delay(clock=40000000)
#use rs232(baud=9600, xmit=PIN_c6, rcv=PIN_c7,errors,enable=pin_b1) // Jumpers: 8 to 11, 7 to 12 |
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ryan.reeve
Joined: 23 Jul 2006
Posts: 20
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| that is included |
| Posted: Mon Nov 27, 2006 1:16 pm |
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| drolleman wrote: | you need #fuses statement
#include <18f252.h>
#device ADC=10
#device *=16
#fuses H4,wdt128,NOPROTECT,NOBROWNOUT,noPUT,NOLVP,debug
#use delay(clock=40000000)
#use rs232(baud=9600, xmit=PIN_c6, rcv=PIN_c7,errors,enable=pin_b1) // Jumpers: 8 to 11, 7 to 12 |
These are contained in another file included in the code, but not shown here. |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Mon Nov 27, 2006 1:37 pm |
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1. Tell us about your GPS. Post the manufacturer and part number.
2. Tell us about your hardware connections between the PIC and GPS.
Describe the circuit.
3. What PIC are you using ?
4. What is your compiler version ?
5. Explain how you know that you're getting garbage. There is nothing
in your program that displays the data. |
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ryan.reeve
Joined: 23 Jul 2006
Posts: 20
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| detail.. |
| Posted: Tue Nov 28, 2006 12:40 am |
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| PCM programmer wrote: | 1. Tell us about your GPS. Post the manufacturer and part number.
2. Tell us about your hardware connections between the PIC and GPS.
Describe the circuit.
3. What PIC are you using ?
4. What is your compiler version ?
5. Explain how you know that you're getting garbage. There is nothing
in your program that displays the data. |
I am using Garmin 12 XL and tried it with 16F877 and 18F452
Compiler is 3.249
I have omitted the print statement as my original purpose is not to print the GPS output butto grab the bearing and send to the servo controller.
I am using Proteus to simulate the circuit. |
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Douglas Kennedy
Joined: 07 Sep 2003
Posts: 755
Location: Florida
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| Posted: Tue Nov 28, 2006 9:52 am |
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Well there is a printf to an LCD statement in the RDA isr it is just echoing a received char but it will take as much time at least as it takes to accept a char and therefore puts the reception of the next char at some risk. There is no circular buffer on the sentence to be received just a linear buffer.
Suggestions:
Remove the linear buffer and replace it with a circular buffer...see the ccs examples and search this board.
Remove the printf to lcd and locate it in main only this time to print whatever is in the new circular buffer.
Unless you screen out other sentences by deslecting them in your GPS receiver them you run the risk of the receive buffer being filled with a sentence you don't want. It will need to be either thrown away promptly in your main routine or the RDA isr will need enhancing to a "count me in" type logic. If you see a $ then the next char must be say "G" then "M" then "P" etc
until your specific sentence is identified only then is it allowed into your circular buffer.
Now a Nmea sentence also has a check digit. If you are using this for any
real navigation you really should check this. It follows the "*" |
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ryan.reeve
Joined: 23 Jul 2006
Posts: 20
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| Posted: Tue Nov 28, 2006 11:38 am |
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| Douglas Kennedy wrote: | | Nmea sentence also has a check digit |
Are u talkin about the checksum ?
what is its importance from navigational point of view.
thanks. |
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ckielstra
Joined: 18 Mar 2004
Posts: 3680
Location: The Netherlands
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| Posted: Tue Nov 28, 2006 1:32 pm |
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| The Garmin GPS 12XL is a stand alone consumer unit. How did you create the connection to your PIC processor? Did you use the Garmin supplied cable or created one yourself? Have you added a MAX232 or similar circuit? |
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ryan.reeve
Joined: 23 Jul 2006
Posts: 20
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| Posted: Wed Nov 29, 2006 12:13 am |
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| ckielstra wrote: | | The Garmin GPS 12XL is a stand alone consumer unit. How did you create the connection to your PIC processor? Did you use the Garmin supplied cable or created one yourself? Have you added a MAX232 or similar circuit? |
I used the standard Garmin cable without MAX232 as it is builtin within 12XL. |
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MarcosAmbrose
Joined: 25 Sep 2006
Posts: 38
Location: Adelaide, Australia
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| Posted: Wed Nov 29, 2006 3:51 am |
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| write the characters to a buffer as they're received by the RDA interrupt. Once you've received a complete NMEA sentence, then print the buffer to your LCD. |
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Douglas Kennedy
Joined: 07 Sep 2003
Posts: 755
Location: Florida
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| Posted: Wed Nov 29, 2006 8:45 am |
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What the checksum does is enable you to know with a high degree of assurabliity that you have received the sentence from your GPS correctly.
An incorrect value possibly could cause an accident. Another thing to be aware of is that the sentence also has a status flag...if the status flag is not indicating a good fix then even if the checksum validates the reading is no good for navigation. |
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