USART đơn giản

[duy.hut.fet]

em co doan code nay sau chi build thi no cu bao la A device required before the line ma e ko biet sua nhu the nao.mong anh em trong dien dan giup do
// 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 5x7 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;
}