I have a problem with this set up .it’s an audio link and uses adc0804 and dac0808 controlled by an 89s52 mcu ,nothing fancy just to send digital encoded audio via rs232 port at barely acceptable quality,when I convert voice and send it to the on board dac sounds fine. But when I try to send and receive from another identical setup (this project went in pair) I began to have all kind of loud parasitics masking the received sound, are there any helps or hints ?
Thanks a lot
Vu nhu Khanh
this is the coding of the setup

$mod52
;equate table for the port and pins
intr bit p1.0 ;ad conversion complete
write bit p1.1 ;adc cycle
read bit p1.2
buzz bit p1.4
bell bit p3.2
talk bit p3.3
digi_in equ p2 ;data in from ADC0804, p2
digi_out equ p0 ;data out from DAC0808, p0
org 00h ; reset vector
ljmp start ;jump to start
org 30h

init_baud:
mov scon,#52h
mov tmod,#20h
mov th1,#0fdh
setb tr1
setb ren

ret

send:
clr ti
mov sbuf,a
ret

receive:
clr ri
mov a,sbuf
ret

dac_convert:
mov digi_out,a
ret

adc_convert:
clr write
setb write
jb intr,$ ;done?
mov a,digi_in ;read this byte
mov digi_out,a ;and send it to p2 digi_out too,to have sort of monitor voice
ret

start:
lcall init_baud
over:
lcall adc_convert
lcall send ;shit hits the fan when sending data
lcall receive ; high hiss noise here
lcall dac_convert
sjmp over

end