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dream10101tysh
Joined: 17 Apr 2013
Posts: 3
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| Problem of using PIC18F458 to receive gps NMEA code |
 Posted: Wed Apr 17, 2013 7:09 am |
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I use pic18f458 to receive gps NMEA message. The objective is to get the latitude , longitude and UTC real time and transmitted via RS232 to RF modem. The problem is that the RDA_ISR is not working after I disable it. I just wanna to check the rcv() function is ran completely. After that, the RDA_ISR is re-enabled. I am a beginner and not sure whether it is possible to use this 8-bit pic to complete this project. Any suggestions are important to me. Thank you!
| Code: |
#include <18f458.h>
#include <stdlib.h>
#fuses HS
#use delay(clock = 20000000)
#use rs232(baud = 9600, xmit = PIN_C6, rcv = PIN_C7)
#priority RDA
#define bsize 128
unsigned char UART_ReceiveBuffer[bsize], UART_IsReceived=0, buf[110], len=0, out[31], header[4]={255,254,253,252},mm;
void rcv()
{
unsigned char ii,jj;
for(ii = 0; ii < len; ++ii)
{
for(jj = 0; jj<110; jj++)
{
buf[jj] = buf[jj+1];
}
buf[109] = UART_ReceiveBuffer[ii];
if(buf[0]==36 && buf[3]==71 && buf[4]==71 && buf[5]==65)
{
unsigned char kk=0;
for(kk=0;kk<6;kk++)
{
out[kk]=buf[kk+7]; //6bytes(UTC)
}
for(kk=0;kk<12;kk++)
{
out[kk+6]=buf[kk+17]; //12bytes(Latitude)
}
for(kk=0;kk<13;kk++)
{
out[kk+18]=buf[kk+30]; //13bytes(Longitude)
}
}
}
len=0;
}
#INT_RDA
void RDA_isr(void)
{
UART_ReceiveBuffer[len] = getc();
++len;
if(len>=120)
UART_IsReceived = 1;
disable_interrupts(GLOBAL);
disable_interrupts(INT_RDA);
}
void main()
{
enable_interrupts(INT_RDA);
enable_interrupts(GLOBAL);
while(TRUE)
{
if(UART_IsReceived==1)
{
UART_IsReceived=0;
rcv();
enable_interrupts(INT_RDA);
enable_interrupts(GLOBAL);
}
printf("%c%c",header[0],header[1]);
for(mm=0;mm<6;mm++)
{
printf("%c",out[mm]);
}
for(mm=6;mm<18;mm++)
{
printf("%c",out[mm]);
}
for(mm=18;mm<31;mm++)
{
printf("%c",out[mm]);
}
delay_ms(1000);
}
}
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Ttelmah
Joined: 11 Mar 2010
Posts: 19454
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| Posted: Wed Apr 17, 2013 7:49 am |
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ERRORS.
Problem is if you disable the UART, and data arrives (it will), the UART goes into an error state, and is locked. The 'ERRORS' keyword, in #use rs232, makes the compiler add code to clear this.
Search the forum.
Other comments:
#priority does nothing unless you have multiple interrupts.
Then you have the big problem that your data won't be where you expect it to be in the stream. Since you have missed characters. Use a circular buffer, and look for the characters that define the start of the message. There are complete code examples for decoding GPS strings here, and in the code library.
Best Wishes |
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