This is an example of a 16 byte averager. Most problems with jittery a/d conversion are due to power supply ripple and bad ground layout. Pay attention to that before you try to stabilize (read: throw away data) in software.

;16 sample average

$mod552
$debug(middel.abs)

bufsize equ 16

dseg

org 040h

pointer: ds 1
totallsb: ds 1 ;16-bits 'running' total
totalmsb: ds 1
bufstart: ds 16 ;newest first, oldest last

cseg

org 0
ljmp init

org 00400h
init: mov pointer,#bufstart ;pointer MUST be in lower 128 RAM

mov r0,#totallsb
clr a
mov b,bufsize+2
initloop: mov @r0,a
inc r0
djnz b,initloop

main: mov r0,#totallsb ;totaal + new value
xch a,@r0
add a,@r0
xch a,@r0
inc r0
xch a,@r0
addc a,#0
xch a,@r0

mov r0,pointer ;New value in bufstart, oldest out
xch a,@r0

xch a,pointer ;update bufstart pointer
inc a
cjne a,#bufstart+bufsize,nowrap
mov a,#bufstart
nowrap: xch a,pointer

mov r0,#totallsb ;totaal - oldest
xch a,@r0
clr c
subb a,@r0
mov @r0,a
inc r0
mov a,@r0
subb a,#0
mov @r0,a

dec r0
mov a,@r0 ;total / 16
anl a,#0f0h
inc r0
orl a,@r0
swap a

;average now in a

end