Global Positioning System is based on satellite navigation technology. A GPS Receiver provides the accurate location of an object in terms of latitude and longitude. Accurate time calculation with respect to GMT can also be done by using GPS. For more information on different data obtained through GPS, refer GPS Receivers. Here a PIC microcontroller has been interfaced with a GPS module to extract its position information (location).
GPS provides a lot of geographical information for a particular object like its latitude, longitude, direction of travel, GMT etc. This information are assembled in a particular string format which are to be decoded by GPS modems. A GPS modem gives the output data in a following string format called as NMEA Format. A common GPS sentence ($GPGGA) has been explained below.
1. Set the baud rate of PIC’s USART to 4800 bps.
Project Source Code
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// Program to Interface GPS with PIC18F4550 Microcontroller
#define FREQ 12000000
#define baud 4800
#define spbrg_value (((FREQ/64)/baud)-1)
#define rs LATA.F0
#define rw LATA.F1
#define en LATA.F2
#define lcdport LATB
unsigned char rx_data();
void lcd_ini();
void lcdcmd(unsigned char);
void lcddata(unsigned char);
unsigned char longi_data[12];
unsigned char lati_data[12];
unsigned char data,value=0;
unsigned int i=0,pos;
void main()
{
TRISB=0; // Set Port B as output port
LATB=0;
TRISA=0;
LATA=0;
SPBRG=spbrg_value; // Fill SPBRG register to set the baud rate
RCSTA.SPEN=1; // To activate serial port (Tx and Rx pins)
RCSTA.CREN=1; // To enable continuous reception
lcd_ini();
while(1)
{
data=rx_data(); // Check the string ‘$GPGGA,’
if(data==’$’)
{
data=rx_data();
if(data==’G’)
{
data=rx_data();
if(data==’P’);
{
data=rx_data();
if(data==’G’);
{
data=rx_data();
if(data==’G’)
{
data=rx_data();
if(data==’A’)
{
data=rx_data();
if(data==’,’)
{
data=rx_data();
while(data!=’,’)
data=rx_data();
for(i=0;data!=’N’;i++)
data=rx_data();
lati_data[i]=data; // Store the Latitude data
}
data=rx_data();
if(data==’,’)
{
for(i=0;data!=’E’;i++)
{
data=rx_data();
longi_data[i]=data; // Store the Longitude data
}
}
i=0;
lcdcmd(0x80);
while(i<11)
{
lcddata(lati_data[i]); // Print the Latitude data
i++;
}
i=0;
lcdcmd(0xC0);
while(i<12)
{
lcddata(longi_data[i]); // Print the Longitude data
i++;
}
}
}
}
}
}
}
}
Delay_ms(1000);
for(i=0;i<12;i++)
{
data=0;
lati_data[i]=0;
longi_data[i]=0;
}
}
}
unsigned char rx_data(void)
{
while(PIR1.RCIF==0); // Wait until RCIF gets low
return RCREG; // Store data in Reception register
}
void lcd_ini()
{
lcdcmd(0x38); // Configure the LCD in 8-bit mode, 2 line and 5×7 font
lcdcmd(0x0C); // Display On and Cursor Off
lcdcmd(0x01); // Clear display screen
lcdcmd(0x06); // Increment cursor
lcdcmd(0x80); // Set cursor position to 1st line, 1st column
}
void lcdcmd(unsigned char cmdout)
{
lcdport=cmdout; //Send command to lcdport=PORTB
rs=0;
rw=0;
en=1;
Delay_ms(10);
en=0;
}
void lcddata(unsigned char dataout)
{
lcdport=dataout; //Send data to lcdport=PORTB
rs=1;
rw=0;
en=1;
Delay_ms(10);
en=0;
}
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Source: How to interface GPS with PIC18F4550 Microcontroller- (Part 16/25)
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