Franc,

Try this routine:

1st prior to processing the string (or your single byte) init both crc_hi & crc_lo = 0FFH
(not for each byte but just prior to the entire record to be handled).

After the entire string has passed byte by byte through the routine. append crc_hi & crc_lo (complimented)

-------------------
crc16:
push ar0
push acc
push psw

; *** Begin the CRC Routine ***

mov r0,#8
xrl crc_hi,a

crc_lp1:
clr c
mov a,crc_lo
rrc a
mov crc_lo,a

mov a,crc_hi
rrc a
mov crc_hi,a
jnc crc_lp2

xrl crc_hi,#08h
xrl crc_lo,#84h

crc_lp2:
djnz r0,crc_lp1

pop psw
pop acc
pop ar0
ret

---------------------

For instance:
----------------
mov crc_lo,#0FFH
mov crc_hi,#0FFH

mov a,#1
call crc16
------------
at this point crc_hi=0EH crc_lo=1EH
if we compliment it ("cpl a") we get *crc_hi=F1
*crc_lo=E1

Now lets do it with 2
-------------

mov crc_lo,#0FFH
mov crc_hi,#0FFH

mov a,#2
call crc16
------------

at this point crc_hi=95H crc_lo=2CH
if we compliment it we get *crc_hi= 6AH
*crc_lo=D3H

regards,
p