#include <16f628A.h>
#fuses INTRC_IO,NOWDT,NOPROTECT,NOBROWNOUT,NOLVP,NOPUT,NOCPD
//#fuses HS  external oscillator
#use delay (clock=4000000)
#use rs232 (baud=9600, xmit=PIN_B2,rcv=PIN_B1, parity=N, stop=1) 

#use fast_io(A)
#use fast_io(B)

#define buton1 pin_a1
#define buton2 pin_a2
#define buton3 pin_a3
#define buton4 pin_a4

   void preamble(){
    putc(0x55);   
    putc(0x00);
    putc(0xff);
    return;
   }


void main(){

  set_tris_a(0xFF);   // Port A is input
  set_tris_b(0x00);   //Port B is output
  output_b(0);     // Cleaining port B
    
while(True)
  {
    preamble();
    
    if(input(pin_a1)==0)  // If pin A1 is zero sent Data of A
    {
    putc('A');
    }
    if(input(pin_a2)==0) // If pin A2 is zero sent Data of B
    {
    putc('B');
    }
    if(input(pin_a3)==0)  // If pin A3 is zero sent Data of C
    {
    putc('C');
    }
    if(input(pin_a4)==0) // If pin A4 is zero sent Data of D
    {
    putc('D');
    }
   }
}