rs232 rx tx

#include <p18f4520.h>
#include <usart.h>
#include <delays.h>
#include <portb.h>

unsigned char c;
unsigned char c1;
unsigned char c2;
unsigned char c3;
unsigned char c4;
unsigned char checksum;
unsigned char m;

  unsigned char i;
  unsigned char b;

void rx_handler (void);//declare the ISR function.HIGH





#define BUF_SIZE 25

/*
 * Step #1  The data is allocated into its own section.
 */
#pragma idata bigdata
char data[8][BUF_SIZE+1] = {
  { "You Typed: 0\n\r" },
  { "You Typed: 1\n\r" },
  { "You Typed: 2\n\r" },
  { "You Typed: 3\n\r" },
  { "You Typed: 4\n\r" },
  { "You Typed: 5\n\r" },
  { "Invalid key (0-5 only)\n\r" }
};


#pragma idata


//location of the ISR.(HIGH)
#pragma code rx_interrupt = 0x8
void rx_int (void)
{
  _asm goto rx_handler _endasm
}
#pragma code  //return to default code section



#pragma interrupt rx_handler
void rx_handler (void)
{



while(!DataRdyUSART());
    c  = getcUSART();//start byte

while(!DataRdyUSART());
    c1  = getcUSART();//add

while(!DataRdyUSART());
    c2  = getcUSART();//cmd

while(!DataRdyUSART());
    c3  = getcUSART();//data

while(!DataRdyUSART());
    c4  = getcUSART();//chksum


checksum = (c1 + c2 + c3 + c4);


if(checksum==0xFF)
{

//OK


(0xFF - (c2 + 0x06 + c3)) == m;


while (BusyUSART());
	//value sent
	putcUSART(0xCE);

while (BusyUSART());
	//value sent
	putcUSART(c3);

while (BusyUSART());
//value sent 
	putcUSART(0x06);

while (BusyUSART());
	//value sent
	putcUSART(c2);

while (BusyUSART());
	//value sent
	putcUSART(m);

        //got a valid package so send acknowledge
        //and use the data
    
}


else{

//NOT OK

unsigned char m;
m = (0xFF - (c3+ 0x21 + c2));


while (BusyUSART());
	//value sent
	putcUSART(0xCE);

while (BusyUSART());
	//value sent
	putcUSART(c3);

while (BusyUSART());
//value sent 
	putcUSART(0x21);

while (BusyUSART());
	//value sent
	putcUSART(c2);

while (BusyUSART());
	//value sent
	putcUSART(m);




}

    //Clear the interrupt flag 
    PIR1bits.RCIF = 0;
}




void main (void)
{
ADCON1 = 0x0F;
TRISCbits.TRISC5 = 0;

//LED
TRISB = 0;



  OpenUSART (USART_TX_INT_OFF &
             USART_RX_INT_ON &
             USART_ASYNCH_MODE &
             USART_EIGHT_BIT &
             USART_CONT_RX &
             USART_BRGH_HIGH, 25);









PORTBbits.RB3 = 1;

PORTCbits.RC5 = 1;
Delay10KTCYx(50);


while (BusyUSART());
	//value sent
	putcUSART(0x31); 

while (BusyUSART());
	//value sent
	putcUSART(0x32);

while (BusyUSART());
//value sent 
	putcUSART(0x33);

while (BusyUSART());
	//value sent
	putcUSART(0x34);

while (BusyUSART());
	//value sent
	putcUSART(0x35);



Delay10KTCYx(50);

PORTBbits.RB3 = 0;
PORTCbits.RC5 = 0;




/* Enable interrupt priority */
  RCONbits.IPEN = 1;

  /* Make receive interrupt high priority */
  IPR1bits.RCIP = 1;

  /* Enable all high priority interrupts */
  INTCONbits.GIEH = 1;

  /* Loop forever */
 while (1)
    ;
}