G'day Steve,

When I did this for my PIC 12C509 based DS1820 to RS-232 device, I
multiplied by nine, divided by five, and then added thirty two.  At
the point in my code that I needed to do it, I had the measurement in
degrees centigrade, scaled by one hundred, in a sixteen bit signed
integer, such that 23.54 degrees is binary value for decimal 2354.

        pushl16 d'9'            ; multiply by nine
        call    sb_multiply

        pushl16 d'5'            ; divide by five
        call    sb_divide       ; (therefore multiply by 1.8)
        call    sb_nip          ; drop remainder

        pushl   d'128'          ; add thirty two (3200)
        pushl   d'12'
        call    sb_add

As you can see, the means by which the solution is expressed is very
simple.  It does depend on my stack math package, which uses an
FSR/INDF stack of data, in the same way that FORTH programmers would
use.  Maybe this is a math library for you? This package is on the
web at

        <http://quozl.netrek.org/stack-math.asm>

Observant types will notice that this conversion will corrupt the
value if the intermediate result after multiplication by nine exceeds
the signed integer size of fifteen bits.  Anything above 36.40 degrees
celcius, or 97.52 degrees fahrenheit, will not be converted properly.

The DS1820 to RS-232 converter is described at

        <http://quozl.netrek.org/ts/>

--
James Cameron    mailto:quozl@us.netrek.org     http://quozl.netrek.org/

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