printf does not work on microcontroller

Exactly how do you know that the baudrate is correct? Have you checked the bit length with an oscilloscope?

A second thing: Are you making sure that the transmit register is empty before you write the next character to it?

When i write that code it works both in simulation and on microcontroller

#include <DS89C4xx.H>

void main (void)
{
  SCON0=0x50;
  TMOD=0x20;
  TH1=0xFC;
  TR1=1;
  TI_0=1;
  while (1)
  {     while (!TI_0);
        if (TI_0==1){
                TI_0=0;
                SBUF0='t';
                }
        while (!TI_0);
        if (TI_0==1){
                TI_0=0;
                SBUF0='e';
                }
        while (!TI_0);
        if (TI_0==1){
                TI_0=0;
                SBUF0='s';
                }
        while (!TI_0);
        if (TI_0==1){
                TI_0=0;
                SBUF0='t';
                }
        }
}

this program writes "testtesttest...". I observe it on Terminal Emulator. This means the baud rate is correct. Unfortunately, when I use printf() instead of sending each character by using SBUF0 it does not work on microcontroller. I cannot observe onTerminal Emulator's screen but i can observe on Keil's Serial Window.

Sounds like you have a bug in your putchar(), then?

I changed all SBUF to SBUF0, RI to RI_0, and TI to TI_0 in PUTCHAR.c and saved as PUTCHAR2.C and add to my source code but it didn't work.

Show the code!

I changed putchar.c in c51/lib to that.

/***********************************************************************/
/*  This file is part of the C51 Compiler package                      */
/*  Copyright KEIL ELEKTRONIK GmbH 1990 - 2002                         */
/***********************************************************************/
/*                                                                     */
/*  PUTCHAR.C:  This routine is the general character output of C51.   */
/*  You may add this file to a uVision2 project.                       */
/*                                                                     */
/*  To translate this file use C51 with the following invocation:      */
/*     C51 PUTCHAR.C <memory model>                                    */
/*                                                                     */
/*  To link the modified PUTCHAR.OBJ file to your application use the  */
/*  following Lx51 invocation:                                         */
/*     Lx51 <your object file list>, PUTCHAR.OBJ <controls>            */
/*                                                                     */
/***********************************************************************/

#include <DS89C4xx.H>


#define XON  0x11
#define XOFF 0x13


/*
 * putchar (full version):  expands '\n' into CR LF and handles
 *                          XON/XOFF (Ctrl+S/Ctrl+Q) protocol
 */
char putchar (char c)  {

  if (c == '\n')  {
    if (RI_0)  {
      if (SBUF0 == XOFF)  {
        do  {
          RI_0 = 0;
          while (!RI_0);
        }
        while (SBUF0 != XON);
        RI_0 = 0;
      }
    }
    while (!TI_0);
    TI_0 = 0;
    SBUF0 = 0x0d;                         /* output CR  */
  }
  if (RI_0)  {
    if (SBUF0 == XOFF)  {
      do  {
        RI_0 = 0;
        while (!RI_0);
      }
      while (SBUF0 != XON);
      RI_0 = 0;
    }
  }
  while (!TI_0);
  TI_0 = 0;
  return (SBUF0 = c);
}



#if 0         // comment out versions below

/*
 * putchar (basic version): expands '\n' into CR LF
 */
char putchar (char c)  {
  if (c == '\n')  {
    while (!TI_0);
    TI_0 = 0;
    SBUF0 = 0x0d;                         /* output CR  */
  }
  while (!TI_0);
  TI_0 = 0;
  return (SBUF0 = c);
}


/*
 * putchar (mini version): outputs charcter only
 */
char putchar (char c)  {
  while (!TI_0);
  TI_0 = 0;
  return (SBUF0 = c);
}

#endif

I changed putchar.c in c51/lib to that.

You may still be linking with the library version of putchar(). Try putting a breakpoint in your putchar() and see if it is being called.

www.maxim-ic.com/.../do

I have a very simple but annoying problem. I use printf () in my code and either on Keil or Proteus simulations it works. However, when I load this code to my microcontroller, which is DS89C450, it does not work.
you say nothing about your hardware, but I do hope you have a MAX232(equivalent) correctly implemented between the uC and the PC.
One poster a long time ago had the same problem and it was using the wrong capacitor values.

since it works on the simulator, I guess hardware or baudrate error.

Erik

you saved it as "PUTCHAR2.C"? you need to save it as "PUTCHAR.C" in your project directory.

No, I think that's wrong:

The name of the file shouldn't matter - it's the name of the function that's important (also its return type & parameter types).

[...] it's the name of the function that's important [...]

Depends a bit on what file name the project file mentions :)

I think i skipped something and that is it: I changed putchar but printf() works with putchar and _getkey so i have to change _getkey by swapping SBUF with SBUF0 and RI with RI_0 AND TI with TI_O too. I have the equipments at firm. So I'm going to try this Monday. If it wouldn't work, I acquaint you with that.

P.S: Thank you all for your care. I hope it works.. :)