8051 microcotroller interfacing with an ultrasonic sensor[assembly]

Im in an assembly language class at NEIT, im very lost and the fellas at saturday help arent much as theyve passed this class long ago.

the lab project calls for me to sound a buzzer if the Ultrasonic sensor senses anything

so far all that it’s doing is buzzing non stop, its not a matter of sensativity or interfence, its something in my code

just need some help, really dont want to fail this class, Id appreciate any help

START:
TOP:      setb P3.6       ; turn on utx
NO:      jb   P3.4, NO
          call beep
          jmp TOP
         

beep:         
            mov R1, #200
             mov TMOD, #01H ;setting timer0 in 16 bit mode
AGAIN:    mov TL0,  #8Dh ; our low value  for our period
             mov TH0,  #0FFh ; our hi value
        Setb TR0     ; starts timer
HERE:    JNB TF0, HERE               ; waits for flag to set
        CLR TR0           ; stops timer
        CPL P0.0      ; toggles switch to create our square wave
         
        CLR TF0        ; clears flag
        DJNZ R1,Again
        ret

        end