Tanks for the reply's on this matter
the thing is what i wand to do is more complicated
I am reading 12 bit of data from an potentiometer when it is in the
middle
it should give something like 0x0800  "hex"
when i turn left it decreases and when i turn right it increases
The maximum increment should be from 0x80 to 0xEF  and the maximum
decrement must not cross 0x00  from0x80 down to 0x00within one reading
if so i have to increment or decrement
with these maximums or less until i reach the last readout.

I hope i am more clear on what i want to do

I can get the data msb first in the registers datahi and datalo but
the LTC1286 allows also to read LSB first

Example   first readout  could be  x0800  the next  0x0880
the differents is 80 positive is bigger than 0x7F so i add 0x7Fto
previous readout
and compare again with the last readout witch can have changed in this
example
i assume not so 0x880 sub 0x87F is 0x01 witch is less than 0x7F and
i add 0x01 to the first readout and the process stops  until a new
readout
appears  to be differend .

I don't understand what is the meaning msb stored at lower adress at the

moment i am
trying simulating this in MacPic



  Storlox     equ   0x10
  Storhix     equ   0x11
  ;Storloy    equ   0x12
  ;Storhiy    equ   0x13
  TmpReg1     equ   0x14
  TmpReg2     equ   0x15
  datalo      equ   0x16
  datahi      equ   0x17



   movlw   0x30
   movwf   datalo
   movlw   0x01
   movwf   datahi
   movlw   0x20
   movwf   Storlox
   movlw   0x01
   movwf   Storhix
   clrf    TmpReg1
   clrf    TmpReg2

sub16

        movf    datalo,W        ; subtract lsbs
        subwf   Storlox,W
        movwf   TmpReg1
        movf    datahi,W        ; subtract msbs
        btfss   status,C        ; including any carry
        incfsz  Storhix,W
        subwf   datahi,W
        movwf   TmpReg2
        btfsc   status,C        ; new smaller?
        goto    smaller         ; yes
        goto    larger          ; no




smaller  movf    TmpReg1,W
         addwf   TmpReg2,W
         btfsc   STATUS,Z
         goto    zero
         bcf     STATUS,Z
         decf    Storlox
         goto    sub16




larger   incf  Storlox
         goto sub16




zero     incf   Storlox
         goto   sub16


I am totaly confused with carry's not going well
this makes me think to do somting in two complement like this
also totaly confusing



  Storlox     equ   0x10
  Storhix     equ   0x11
  ;Storloy    equ   0x12
  ;Storhiy    equ   0x13
  TmpReg1     equ   0x14
  TmpReg2     equ   0x15
  datalo      equ   0x16
  datahi      equ   0x17



   movlw   0x30         ; new lowByte
   movwf   datalo       ;
   movlw   0x01         ; new highByte
   movwf   datahi
   movlw   0x20         ; old lowByte
   movwf   Storlox
   movlw   0x01         ; old highByte
   movwf   Storhix
   clrf    TmpReg1      ; Store diff
   clrf    TmpReg2      ; Store diff



    comf    datalo,W     ; two complement lowbyte
    addlw   0x01
    movwf   datalo
    ;btfsc   STATUS,C
    ;incfsz  datahi
    comf    datahi,W     ;two complement higbyte
    addlw   0x01
    movwf   datahi

cmp16
    movf    datalo,W     ; datalo>W
    addwf   Storlox,W    ; add oldlobyte
    movwf   TmpReg1      ; store difference
    movf    datahi,W     ; get new higbyte
    btfsc   STATUS,C     ; test carry ifso
    incfsz  Storhix,W      ; incf oldhighbyte
    addwf   Storhix,W
    movwf   TmpReg2
    btfss   STATUS,C
    goto    smaller         ; yes
    goto    larger          ; no



smaller  movf    TmpReg1,W
         addwf   TmpReg2,W
         btfsc   STATUS,Z
         goto    zero
         bcf     STATUS,Z
         decf    Storlox
         goto    cmp16




larger   incf  Storlox
         goto   cmp16




zero     incf   Storlox
         goto   zero

I realy need help on this

 Marcel Elektronic workshop
 Amsterdam