Steve,

I'm doing this (exactly, in fact, down to the DS1620).  You can download
the whole thing from the PICLIST project file archive.  I hope this
is somewhat helpful.  Please bear in mind that it was really my
first shot at C with a compiler that had some pretty severe
restrictions on complex statements, so it looks as bad as it really
is 8-P.   Here's what I do in C:

void read_1620_temp_F() {
    read_1620_temp_C();         //get Celsius temperature
        DS1620_data >>= 1;      //Round up, since .5C=.9F
        DS1620_data *= 9;       //((F*9)/5)+32 = C
        DS1620_data /= 5;       //
        DS1620_data += 32;      //
        Carry = 0;              // Clear carry bit
        DS1620_data <<= 1;      //Shift left again.  This
                                // restores the LSB for the
                                // ASCII conversion later!
}

And in assembler, courtesy of CC5Xfree - there may be more elegent ways to
do it, especially since DS1620_data is a 16-bit variable.  It holds a
9-bit temperatire reading from the DS1620, from which I drop the last bit
before doing the conversion, since it's the .5C bit which equates to
about .9F.  One could probably chop quite a bit of code off of this if one
were doing it all in assembler.

                        ;void read_1620_temp_F() {
read_1620_temp_F
                        ;       read_1620_temp_C();// get Celsius temperature
        CALL  read_1620_temp_C
                        ;       DS1620_data >>= 1;// Round up, since .5C=.9F
        BCF   0x03,Carry
        RRF   DS1620_data+1,1
        RRF   DS1620_data,1
                        ;       DS1620_data *= 9;// ((F*9)/5)+32 = C
        BCF   0x03,Carry
        RLF   DS1620_data,W
        MOVWF C2tmp
        RLF   DS1620_data+1,W
        MOVWF C2tmp+1
        MOVLW .4
        MOVWF C1cnt
m006    MOVF  C2tmp+1,W
        ADDWF DS1620_data+1,1
        MOVF  C2tmp,W
        ADDWF DS1620_data,1
        BTFSC 0x03,Carry
        INCF  DS1620_data+1,1
        DECFSZ C1cnt,1
        GOTO  m006
                        ;       DS1620_data /= 5;//
        MOVF  DS1620_data,W
        MOVWF C4tmp
        MOVF  DS1620_data+1,W
        MOVWF C4tmp+1
        CLRF  C5rem
        MOVLW .16
        MOVWF C3cnt
m007    RLF   C4tmp,1
        RLF   C4tmp+1,1
        RLF   C5rem,1
        BTFSC 0x03,Carry
        GOTO  m008
        MOVLW .5
        SUBWF C5rem,W
        BTFSS 0x03,Carry
        GOTO  m009
m008    MOVLW .5
        SUBWF C5rem,1
        BSF   0x03,Carry
m009    RLF   DS1620_data,1
        RLF   DS1620_data+1,1
        DECFSZ C3cnt,1
        GOTO  m007
                        ;       DS1620_data += 32;//
        MOVLW .32
        ADDWF DS1620_data,1
        BTFSC 0x03,Carry
        INCF  DS1620_data+1,1
                        ;       Carry = 0;// Clear carry bit
        BCF   0x03,Carry
                        ;       DS1620_data <<= 1;// Shift left again.  This
        BCF   0x03,Carry
        RLF   DS1620_data,1
        RLF   DS1620_data+1,1
                        ;// restores the LSB for the
                        ;// ASCII conversion later!
                        ;}
        RETURN





On Thu, 20 Jul 2000, Kosmerchock, Steve wrote:

> Friends,
>
> I am wanting to do a temperature measurment project that
> reads a DS1620 and will display between Celsius and Fahrenheit.
> Has anybody ever done anything like this before on a PIC?
> To convert from C to F you use:
> F=(C*1.8)+32
>
> To convert from F to C you use:
> C=(F-32)/1.8
>
> I have never tried to do multiplication and
> division on a PIC. Does anybody have any advice or
> some code I could look at. I have looked at the
> math library for the PIC, but I am hoping some
> of you PIC math gurus (Scott, Andy, Andrew,....etc.)
> could give me an example. I appreciate your help very much!
>
> Best regards,
> Steve
>
>
> Steven Kosmerchock
> Radio Frequency Systems
> Phoenix  Arizona  USA
> www.rfsworld.com
>
> www.geocities.com/researchtriangle/lab/6584
>
> --
> http://www.piclist.com hint: To leave the PICList
> mailto:piclist-unsubscribe-request@mitvma.mit.edu
>

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