ultrasonic distance finder with 8051

ultrasonic 8051

hi ,i will create a project distance finder with 89c51 and ultrasonic sensor.i use assembly language.but i have any problem.i create a40khz freq and send it then i start timer and with first trigger in reciver i stop timer.i obtain 2 value in TL1,TH1.well i want conver 2 byte
TH1,TL1 to a word and then (word/2) * 340(speed of sound) and show in seven segment.i write afew program but i cant commpleate calculate and show TH1,TL1. please commpleate it or help me.plzzzzzzzzzzzz

ORG 0H
MOV P0,#0FFH
MOV P1,#0
LJMP MAIN

ORG 0013H
SETB TR1
HERE: JNB INT1,HERE
CLR TR1
MOV R0,TL1
MOV R1,TH1
LJMP CAL



;====================FREQ=========
FREQ: SETB TR0
H: JNB TF0,H
CLR TR0
CLR TF0
CPL P2.0
SJMP FREQ





;============MAIN========
ORG 30H
MAIN: MOV IE,#10000100B
MOV TMOD,#12H
MOV TH0,#-12
MOV TL1,#0
MOV TH1,#0
F: JB P0.0,F
SJMP FREQ
;===============CALCULATE=======
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distance+avr+basic+ultrasonic

any idea

Added after 53 minutes:

i want just, just ,just 8051 project..

ultrasonic+8051

HI
I coulden't understand your problem.
is it in 16 bit multiplyand division calculations?

distance measurement 8051

avr is better try it too!

‌ultrasonic 8051

I think (word/2) * 340(speed of sound) is wrong unless you have seconds in TH1,TL1, and I don't think you do.