mov   SCON,#52h    ;set serial mode 1 + preset ti
   mov   TMOD,#21h    
   mov   TH1,#-12     ;2400@11.0592MHz
   setb  tr1          ;enable timer 1
   mov   t2con,#20h   ;only RCLK

   mov   sp,#7
   push  sp

   jnb   ti,$
   clr   ti
   mov   sbuf,8
   jnb   ti,$
   clr   ti
   pop   sp
   mov   sbuf,sp
stop:
   ljmp  stop
   end