Putchar in Keil C, take 8051 as an instance

#define FCLK           22118400UL  
#define BAUDRATE        9600UL            





/* ref http://csserver.evansville.edu/~blandfor/EE354/SFRegisters.pdf */

void InitUART(void)
{
 EA = 0; 
 TMOD &= 0x0F;  /*timer 1 clean*/
 TMOD |= 0x20;  /*mode 2: 0~255,  auto-reload */

 REN = 0; /*forbid 8051 receive data*/
   SM1 = 1; /* Serial Control Register be set by timer*/

 /*
  BaudRate = OscillatorFreq/(N*256-TH1) 
  if SMOD = 0, N = 384
  if SMOD = 1, N = 192 

  SMOD is PCON.7  , Serial mode bit
 */
 
 TH1 = 256 - FCLK/(BAUDRATE*12*16);  
 TL1 = 256 - FCLK/(BAUDRATE*12*16);
 PCON |= 0x80;


 ES = 1;  /*Enable Serial port interrupt */
 REN = 1;   /*allow 8051 receive data */
 EA = 1;   /*Enable interrupt*/     
 

 TI = 1; /* the transmitting has been done */
 RI = 0; /* the receiving is not done yet */

 TR1 = 1;  /*Timer 1 is turned on*/
}/*InitUART*/




void UartInterrupt(void) interrupt 4
{
#if(0)
 if(RI)    
 {   
 }
 else     
 { 
 }
#endif

}/*UartInterrupt*/


char putchar(char c)  
{
 /* \n -> \r\n
   \r -> carriage return, 13
 */

 if (‘\n‘ == c)  
 {
  SBUF = 0x0d;  
   
  while(0 == TI);
  TI = 0;
 } 

 SBUF = c;  
 while(0 == TI);

 TI = 0;

   return c;
}/*putchar*/