GPS receiving problem with pic 16f877a

[pathmasugu]

hi ,
i want to interfacing GPS with pic16f877a, i have complete my code, but while i test my code in project board,i can receive data from GPS one time only..receiver interrupt routine execute one time only ..i have problem in receiv. pls help me...
i have include my program here............


#include <16f877a.h>
#use delay(clock=20000000)
#fuses HS,NOWDT
#byte porta=0x05
#byte portb=0x06
#byte portc=0x07
#byte portd=0x08
#byte porte=0x09
#byte trisa=0x85
#byte trisb=0x86
#byte trisc=0x87
#byte trisd=0x88
#byte trise=0x89
#BYTE PIR1=0X0C
#BYTE PIE1=0X8C
#BYTE RCREG=0X1A
#BYTE INTCON=0X0B
#BYTE TXSTA=0X98
#BYTE SPBRG=0X99
#BYTE RCSTA=0X18
#BIT GIE=INTCON.7
#BIT PEIE=INTCON.6
#BIT RCIF=PIR1.5
#BIT RCIE=PIE1.5

#bit rs=0X08.6
#bit en=0X08.7



void LcdCommandWrite(int8 com);
void LcdDatawrite(int8 data);
void LcdInit();
int i=0,j,flag=0,REC_FLAG=0;
int8 data[77],test[]="$GPGGA,";


#INT_RDA
void rx_data(void)
{
data[i]=RCREG; // Store data in Reception regist
i++;
}


void main() //Main entry
{

GIE=PEIE=RCIE=1;
RCSTA=0X90;
RCREG=0X00;
PIE1=0X20;
TXSTA=0X00;
SPBRG=0X1F;

trisb=0x00;
trisd=0x00;
trisc=0x80;


Lcdinit();
while(true)
{
if(i==77)
{
GIE=PEIE=RCIE=0; // disabling interrupt
for(j=0;j<7;j++)
{
if(data[j]==test[j])
flag=1;
else
flag=0;
}
if(flag==1)
{
LcdCommandWrite(0x80);
for(i=18;i<=28;i++)
{
LcdDatawrite(data[i]);
}
LcdCommandWrite(0xc0);
for(i=30;i<=41;i++)
{
LcdDatawrite(data[i]);
}

//delay_ms(1000);
for(i=0;i<=77;i++)
{
data[i]=0;
}
flag=0;
GIE=PEIE=RCIE=1; //enabling interrupt
i=0;


}

}

}


}


void LcdInit()
{
LcdCommandWrite(0x38);
LcdCommandWrite(0x0c);
LcdCommandWrite(0x06);
LcdCommandWrite(0x01);
LcdCommandWrite(0x80);
}
void LcdCommandWrite(int8 com )
{
rs=0;
portb=com;
en=1;
delay_ms(1);
en=0;
}
void LcdDatawrite(int8 data)
{
rs=1;
portb=data;
en=1;
delay_ms(1);
en=0;
}
_________________
ROCK RAJ

[Ttelmah]

1) Don't duplicate post.
2) Use the CCS functions (getc, putc etc..).
3) Learn to use the code buttons.
4) The reason is that if data arrives while your interrupts are disabled, this will hang the UART, so it stops working. If you use the CCS RS232 functions with 'ERRORS' in the #use rs232 command, the compiler will automatically add code to clear this problem. Also it'll get the baud rate calculation right. You are currently running at 9765.625 baud...
Generally, 'reconsider'. Leave the interrupt enabled, and use a circular buffer. This way data that arrives in the long time needed to update the LCD, won't be lost.
As it is the code will no longer hang if you use the CCS functions, but the data will still have been lost, so the 'count' based input method will no longer be synchronised to the data....

[pathmasugu]

THANKING YOU FOR YOUR REPLY SIR,
I changed my code what you suggest me,still no improvement in my code and one more thing is i got some warning like variable never used :rs232_error.

I referred PCW C Compiler Reference Manual.
ERRORS Used to cause the compiler to keep receive errors in the variable RS232_ERRORS and to reset errors when they occur.
_________________
ROCK RAJ

[Ttelmah]

the RS232ERRORS message, is a warning, not an error. When it adds the error handler it generates a variable, so you _can_ tell what has happened. This causes a warning unless you use it. A search here will find all about it.

Have you switched to flex_lcd?.

Read this comment:

"I really would suggest rethinking the approach, since it still won't work, because the characters may have been missed during the slow LCD operations. However it may well work if you switch to using the flex_lcd driver, since this is much faster than your code...."

Note 'may well'. Not 'will'.

[pathmasugu]

sir,
i dont have any idea about flex_lcd driver ..... pls give some tips
_________________
ROCK RAJ

[Mike Walne]

[ezflyr]

Pathmasugu,

You started off by posting some code that is about as far from the 'CCS-Way" as you can get, and now you 'don't have any idea' about a driver (flex_lcd) that is very ubiquitous here on the forum. Rather than parachuting in here with a million questions, may I suggest that you spend a bit of time with (1) the CCS manual, and (2) the forum archives. Do a bunch of reading to bring yourself up to speed, otherwise your reign here, like many other 'newbies' before you, will be short and sweet......

Cheers,

John

[pathmasugu]

Thanking you for your advice sir ...I'm the beginner of CCS..... now I'm start to study those things....i will contact soon through forum... and also thanks to Mr. Mike for your information.
_________________
ROCK RAJ

[Ttelmah]

One thing that is fundamentally going to cause problems is the 'count' approach.

Yes, count through an individual packet, but you are ignoring, extra characters that may be there (most packets from GPS's etc., will have extra characters - line feed, carriage return etc.), and with the missing character(s) because of your slow LCD handling. These mean you will go 'out of sync'. This is the whole 'point' of the header ($GPGGA). The 'reliable' approach, is to write the code to keep looking for the '$', and at this point reset the counter. Then check that the next set of characters are the 'GPGGA' header, and then retrieve what you want. This way, if there are extra characters, or characters are missed, the code will 're-synchronize' at the next header.
Assuming that characters will never be missed, or that there are no extra characters, is always an unreliable way to work....

A state machine, that searches for the header (search here), is the normal 'good' approach.

[pathmasugu]

_________________
ROCK RAJ

[ezflyr]

Hi,

Hmmm, since YOU came her looking for our help, why not 'pay it forward', and post your working code so that others like you might benefit from it?

John

[pathmasugu]

ya sure ,