find TH1 in AT89s52 micro controller in serial communication
All of the following information is available in Atmel 8051 Microcontrollers Hardware Manual which is referenced in Section 9 of the AT89S52 datasheet as the place to look for information on Timers 0 and 1.

Note: I'm assuming what you have in the comments is what you are trying to do.

First off, your formula is wrong. If you're trying to use Mode 1, SMOD doesn't enter into it. Even so, SMOD is in PCON which you are not setting (which MikeJ-UK mentioned).


  The baud rate in Mode 0 is fixed:
  
  The baud rate in Mode 2 depends on the value of bit SMOD in Special
  Function Register PCON.
  
  If SMOD = 0 (which is its value on reset), the baud rate is 1/64 the
  oscillator frequency. If SMOD = 1, the baud rate is 1/32 the
  oscillator frequency.
  
  In the 80C51, the baud rates in Modes 1 and 3 are determined by the Timer 1 overflow rate. In case of Timer2, these baud rates can be
  determined by Timer 1, or by Timer 2, or by both (one for transmit and
  the other for receive).


Emphasis mine.

Next, your SCON does not match the comment:



You have:

SCON = 0x50

Which equates to:

 FE SM0 SM1 SM2 REN TB8 RB8 TI  RI
 0   1   0   1   0   0   0   0   0


So you're in Mode 2, 9-bit UART with the baud rate given as:

FCPU PERIPH /32 or /16

And serial reception disabled.

And then you've got:

TI = 1

Which you shouldn't do. You clear the interrupt flag. It's set by hardware.

Figure out exactly what you want to achieve and have a good look through those manuals. You'll probably need to rework your formula, change SCON and then set TH1 and TL1.