dear mr erik. sorry i take the impolite comment back
-clock 11.0592
i did try serial communication interrupt same thing !

$mod52

;ñaët teân cho caùc coång vaø caùc pin cuûa maùy, caùc label duøng tieáng Anh cho baûnh !

intr bit p1.0
write bit p1.1
read bit p1.2
buzz bit p1.4
bell bit p3.2
talk bit p3.3
digi_in equ p2
digi_out equ p0

org 0000h ;vectô reset
ljmp start ;nhaåy tôùi start
org 0023h
ljmp tx_rx
org 0030h

init_baud: ;chuaån bò nghi thöùc truyeàn : 9600 baud,8 bit
mov psw,#00h
mov th1, #0fdh
mov scon, #01010000b ;nghi thöùc laø 8 bit uart
mov tmod, #00100001b ;ñaët timer1 chaïy 8 bit
setb tr1
setb ea
setb es
setb ren
setb ti
ret

tx_rx:
jnb ri,check_send
mov a,sbuf
clr ri
check_send:
jnb ti,check_send
mov sbuf,a
exit_int:
clr ti
reti

;

adc_convert:
clr write
setb write
jb intr,$
mov a,digi_in
setb ti
ret



dac_convert:
mov digi_out,a ;chæ caàn ñöa data ñaõ ret ;laø xong



start:
clr ti
lcall calling
start1:
lcall init_baud
again:
lcall adc_convert
lcall dac_convert
sjmp again

end
sorry for the comment my language use funny charactern!