Myslis neco takoveho:

;-------------------------------------------------------------------------------
;Miro - HEX kalkulator
;------------------------------------------------------------------------------
.code
.equ oper,127
.equ vyse,126

Start:
mov p1,#0
mov oper,#0
mov vyse,#0
clr c

Cteni:
mov a,p3
anl a,#b'00001111
mov oper,a
jb p3.4,Soucet
jb p3.5,Rozdil
jb p3.7,Nulov
ajmp Cteni

Soucet:
addc a,vyse
mov vyse,a
ajmp Zobraz

Rozdil:
mov a,vyse
subb a,oper
mov vyse,a

Zobraz:
mov p1,vyse

Tlacit:
jb p3.4,Tlacit
jb p3.5,Tlacit
ajmp Cteni

Nulov:
mov vyse,#0
mov p1,#0
clr c
jb p3.7,Nulov
ajmp Cteni
.end

je to psano pro Atmel AT89C2051 ale melo by to fungovat na vsem podobnem