#include "C:\Users\Ali Ensar TERZİ\Documents\CCS C WORKSPACE\rs232 denemesi\main.h" 
  #use rs232(baud=9600, xmit=PIN_c6, rcv=pin_c7,uart1) 
   
  long gelen=0; //kesme ile gelen data 
   
  set_tris_d(0x00); 
  enable_interrupts(GLOBAL); 
   
  while(1) 
  { 
  enable_interrupts(INT_RDA); 
  output_high(pin_d0); 
  delay_us(gelen); 
  output_low(pin_d0); 
  delay_ms(20); 
  } 
   
  #INT_RDA 
  void seri_data_geldi() 
  {    
  disable_interrupts(INT_RDA); 
     gelen=getch(); 
     gelen=gelen*10; 
  } 
  

 
  public void send(byte data) 
          { 
              if (serialPort1.IsOpen) 
              { 
                  byte[] buffer = { 0 }; 
                  buffer[0] = data; 
                  serialPort1.Write(buffer, 0, 1); 
              } 
              else 
              { 
                  MessageBox.Show("Port açık değil", "Hata!"); 
   
              } 
          } 
  

Sorun osilatörün kondansatöründen kaynaklanıyormuş. Değiştirince düzeldi. Teşekkürler herkese.

 
  #include "C:\Users\EmteR\Documents\CCS C WORKSPACE\PWM Generator 16f877\main.h" 
  #use delay(clock=20000000) 
   
  void main() 
  { 
     double yak=50000; 
     double sondur=50000; 
     setup_adc_ports(NO_ANALOGS); 
     setup_adc(ADC_OFF); 
     setup_psp(PSP_DISABLED); 
     setup_spi(SPI_SS_DISABLED); 
     setup_timer_0(RTCC_INTERNAL|RTCC_DIV_1); 
     setup_timer_1(T1_DISABLED); 
     setup_timer_2(T2_DISABLED,0,1); 
   
     while(1) 
     { 
        output_high(pin_d0); 
        delay_ms(yak); 
        output_low(pin_d0); 
        delay_ms(sondur);      
     } 
  } 
  

#use rs232(baud=9600, xmit=PIN_c6, rcv=pin_c7,uart1) 
  #byte INTCON=0x0C 
  #byte PIE1=0x8C 
  #use fast_io (b) //trisleri kendimiz ayarlayalim 
  #use fast_io (d) 
  long bx; //kesme ile gelen data 
   
  void main() 
  { 
  setup_adc_ports(NO_ANALOGS); 
     setup_adc(ADC_OFF); 
     setup_psp(PSP_DISABLED); 
     setup_spi(SPI_SS_DISABLED); 
     
     setup_timer_1(T1_DISABLED); 
  INTCON=0x3000000; //global ve peripheral kesmeler aktif 
  PIE1=0b00100000; //uart kesmesi ayarlandı kesmeler aktif 
   
   
   
  #INT_RDA 
  void seri_data_geldi(){ 
  bx=getc(); 
   
  if(bx==123) 
  output_high(pin_d0); 
  if(bx==132) 
  output_low(pin_d0); 
   
  }