Option EXPLICIT

const maxto = 500  'exemple time out 5 sec
dim cptto as integer  'count time$
dim flgeot as integer

SETTICK 10,sptim
Open "COM1:9600,255,spcomrec" As #2

flgeot=0


do

'  if need to read serial
 cptto=maxto
 ....
 if flgeot=1 then
flgeot=0
.....   'task receive text
 end if
'
...
'if no need read serail
 cptto=0
 

loop

sub sptim
 if cptto>0 then  'if cptto=0 then do nothing
   cptto=cpto-1
   if cptto=0 then 'if end of time-out do task "timeout"
     ....
   end if
 end if
end sub

sub spcomrec
Local tx$ As string
Local i2 As integer
Local a$ As string length 1
 nbcar=Loc(#2)
 If nbcar>0 Then
   tx$=Input$(nbcar,#2)
     cptto=maxto
     'do task read serial
       'exemple
       For i2=1 To nbcar
         a$=Mid$(tx$,i2,1)
         If (asc(a$)=13 or asc(a$)=10) Then  'end rec texte
             .....
           flgeot=1
         end if
       next i2
 end if
end sub