> 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 no more than 0x3f  from 0x00 on and the
> maximum
> decrement must not cross from  0x7F  down to  0x40 within 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  0x0870
> the different is 70 positive is bigger than 0x3f so i add 0x3f to
> previous readout
> and compare again with the last readout witch can have changed in this
> example
> i assume not so 0x870 sub 0x83f is 0x31 witch is less than 0x3f  and the
> process stops
> until a new readout appears
>
> I don't understand what is the meaning msb stored at lower adress at the
> moment i am
> trying simulating this in MacPic
>
>   Storage1      equ   0x10
>   Storage2      equ   0x11
>   Storage3      equ   0x12
>   Storage4      equ   0x13
>   TmpReg1     equ   0x14
>   TmpReg2     equ   0x15
>   datahi           equ   0x16
>   datalo           equ   0x17
>
>    movlw         0x01         ;
>    movwf        datalo       ;
>    movwf        Storage1     ;
>    movlw         0x80         ;
>    movwf        datahi       ;
>    movwf        Storage2     ;
>    clrf             TmpReg1      ;
>    clrf             TmpReg2      ;
>
> start
>
>   ; movwf       Storage1
>   ; movwf       TmpReg1
>
>    movf            datahi,W
>    subwf          Storage2,W
>    movwf         TmpReg2
>    btfss             STATUS,Z
>    decf              TmpReg1,F
>    movf             datalo,W
>    subwf           TmpReg1,F
>   ; incf               datalo
>
>    goto              start
>
> As i already  sad    thanks  for all the reply's on this matter

The decrement steps can vary from 7f to 41 and increment steps from 0x00to
0x3f

I had some difficulty whit sending email and found out later that
i had send the same message several times sorry for that.

Philip has some USB chips with I2C interface maybe interesting for
PIC USB  The protockol for usb is in hardware on the chip


>
>
> Marcel   Electronic  Workshop Scope
>
> Amsterdam .