How to control PWM Frequency on Mcs-51(AT89C51AC3)

[kioperapong]

I use PWM on Msc-51.

But i can't Control Frequency.

I want 20Khz

CCON       DATA    0XD8 
CMOD       DATA    0XD9 
CCAPM2     DATA    0XDC 
CL         DATA    0XE9 
CH         DATA    0XF9 
CCAP2L     DATA    0XEC 
CCAP2H     DATA    0XFC 
CF         BIT     CCON.7 
CR         BIT     CCON.6 

;===================================================================================== 
   ORG 0000H  
MAIN:
   MOV CL,#08H 
   MOV CH,#08H 
   MOV CCAP2L,#04CH		 //Duty 70%
   MOV CCAP2H,#04CH               //Duty 70%
   MOV CMOD,#02H	   
   MOV CCAPM2,#042H	   
   SETB CR                
   JMP $
   END