Grant,
To divide efficiently by 13.18 use a constant division/multiplication
code generator at
www.piclist.com/codegen/constdivmul

This is as easy as copy and paste :)

; ACC = ACC * 0.075900
;
; ALGORITHM:
; Clear accumulator
; Add input / 16 to accumulator
; Add input / 64 to accumulator
; Substract input / 512 from accumulator
; Move accumulator to result
;
; Error in constant approximation : 0.358202, %


; Input:  ACC0 .. ACC1  (11 bits)
; Output: ACC0  (8 bits)

        cblock
        ACC0
        ACC1
        TEMP0
        TEMP1
        endc

        movf    ACC0, w
        movwf   TEMP0
        movf    ACC1, w
        movwf   TEMP1
        clrc
        rrf     ACC1, f
        rrf     ACC0, f
        clrc
        rrf     ACC1, f
        rrf     ACC0, f
        clrc
        rrf     ACC1, f
        rrf     ACC0, f
        clrf    ACC1
        comf    ACC0, f
        comf    ACC1, f
        incf    ACC0, f
        skpnz
        incf    ACC1, f
        movf    TEMP0, w
        addwf   ACC0, f
        movf    TEMP1, w
        skpnc
        incfsz  TEMP1, w
        addwf   ACC1, f
        clrc
        rrf     ACC1, f
        rrf     ACC0, f
        clrc
        rrf     ACC1, f
        rrf     ACC0, f
        movf    TEMP0, w
        addwf   ACC0, f
        movf    TEMP1, w
        skpnc
        incfsz  TEMP1, w
        addwf   ACC1, f
        rrf     ACC1, f
        rrf     ACC0, f
        clrc
        rrf     ACC1, f
        rrf     ACC0, f
        clrc
        rrf     ACC1, f
        rrf     ACC0, f
        clrc
        rrf     ACC1, f
        rrf     ACC0, f

; Generated by www.piclist.com/cgi-bin/constdivmul.exe (version March 21, 2000)
; Sat Apr 22 03:50:56 2000 GMT


Hope it helps,
 Nikolai
 http://techref.massmind.org/member/NG--944

On Friday, April 21, 2000 Caisson wrote:
>> Van: Grant Forest <gforest@NETSPACE.NET.AU>
>> Aan: PICLIST@MITVMA.MIT.EDU
>> Onderwerp: Frequency Conversion
>> Datum: vrijdag 21 april 2000 11:35
>>
>>  Goodday,
>>
>>  Spent the last 8 hrs trying to convert a frequency  with a range of
> 7351Hz
>>  to 6033Hz  so that I can display 0 to 100.
>> Can someone point me to a URL that has routines to convert
>>  frequency to decimal. Or do I just do it with a very large lookup table.

> Looks like you could :  Subtract the base frequency (6033) from the one
> you've got, and divide the result by the difference between the highest &
> lowest frequency's (7351 - 6033 => 1318) divided by 100 (1318 / 100 =>
> 13.18).

> You could replace the division by 13.18 by multiplication by 4972 (100 *
> 65536 / 1318), giving a 3-byte result with the percentage in the third byte
> from the right.  This will be easier (multiplying versus division), and
> will deliver a quite accurate result.

> Regards,
>   Rudy Wieser