Организация заданных интервалов времени (8051; ассемблер; multisim)

$MOD51 ;
jmp start        ;goto mark "start"
org 0bh          ;interruption subprogram of the timer T0 overflow 
clr tcon.4       ;prohibit count of the timer
reti             ;return from interruption
 
org 20h 
start:           ;main program
clr c            ;carry reset
mov tmod,#01h    ;setting up T/C0 on the 1st work mode (as a timer) 
setb ie.7        ;general permission of interruptions
setb ie.1        ;permittiong interruption of T/C0 timer
mov p1,#0h       ;setting port P1 for information output
met1: 
mov a,7h         ;moving 7h in ACC for LED1 (7th pin) diode enabling 
mov r0,#28h      ;r0 - cycle counter (28h=40 decimal) -> 40 times * 50 ms = 2 seconds
met: 
mov TL0, #low(not(50000-1)) ;moving lower byte of 50000 to the TL0 register (counting from -50000 to 0)
mov TH0, #high(not(50000-1)) ;moving higher byte of 50000 to the TL0 register (counting from -50000 to 0)
 
mov p1,a         ;enable 7th diode
setb tcon.4      ;enable timer T/C0
next: 
jnb tcon.5, next ;wait for TF0 flag overflow
djnz r0,met      ;cycling 40 times (2 seconds)
rlc a ;
 
mov r0,28h       ;setting the cycle counter again
jnc met          ;if not carry go to "met" 
clr c            ;carry reset
jmp met1         ;infinite cycle
end