ON 20070820@12:20:46 PM at page:
http://www.piclist.com/piclist/codegen/constdivmul.htm#39313.1049768519
James Newton[JMN-EFP-786] removed post 39313.1049768519

|Delete '<A TITLE="P-68.42.38.183" NAME="39313.1049768519" HREF="mailto:steidley@comcast.net">steidley@comcast.net</A> <BLOCKQUOTE><A NAME="68.42.38.183">
</A> 
I am converting the Celsius output of a DS1620 to Fahrenheit.  So,  noting the 5/9 = 1.8 I thought I would give the code generator a try.  Basically, the only thing I changed from the default values is Multiply by Constant value... which of course I entered 1.8.<BR>
<BR>
This is the code it generated, plus a few additions to set ACC0 with a starting value, and code at the end to sit there and loop.  Here it is:<BR>
<BR>
; ACC = ACC * 1.8<BR>
; Temp = TEMP<BR>
; ACC size = 8 bits<BR>
; Error = 0.5 %<BR>
; Bytes order = little endian<BR>
; Round = no<BR>
<BR>
; ALGORITHM:<BR>
; Clear accumulator<BR>
; Add input * 2 to accumulator<BR>
; Substract input / 4 from accumulator<BR>
; Add input / 32 to accumulator<BR>
; Add input / 64 to accumulator<BR>
; Move accumulator to result<BR>
;<BR>
; Approximated constant: 1.79688, Error: 0.173611 %<BR>
<BR>
;     Input: ACC0, 8 bits<BR>
;    Output: ACC0 .. ACC1, 9 bits<BR>
; Code size: 29 instructions<BR>
<BR>
	cblock 0x020<BR>
	ACC0<BR>
	ACC1<BR>
	TEMP0<BR>
	TEMP1<BR>
	endc<BR>
<BR>
; added this just to get a value into ACC0 for testing<BR>
	movlw	21<BR>
	movwf	ACC0<BR>
<BR>
;copy accumulator to temporary<BR>
	movf	ACC0, w<BR>
	movwf	TEMP0<BR>
<BR>
<BR>
;shift accumulator right 1 times<BR>
	clrc<BR>
	rrf	ACC0, f<BR>
<BR>
;add temporary to accumulator<BR>
	addwf	ACC0, f<BR>
<BR>
;shift accumulator right 3 times<BR>
	rrf	ACC0, f<BR>
	clrc<BR>
	rrf	ACC0, f<BR>
	clrc<BR>
	rrf	ACC0, f<BR>
<BR>
;substract temporary from accumulator<BR>
	subwf	ACC0, f<BR>
<BR>
;shift accumulator right 2 times<BR>
	rrf	ACC0, f<BR>
	movlw	0x80<BR>
	xorwf	ACC0, f	;invert bit shifted from carry<BR>
	rlf	ACC0, w<BR>
	rrf	ACC0, f<BR>
<BR>
;shift temporary left 1 times<BR>
	clrc<BR>
	rlf	TEMP0, f<BR>
	clrf	TEMP1<BR>
	rlf	TEMP1, f<BR>
<BR>
;add temporary to accumulator<BR>
	clrf	ACC1<BR>
	btfsc	ACC0, 7<BR>
	comf	ACC1, f<BR>
	movf	TEMP0, w<BR>
	addwf	ACC0, f<BR>
	movf	TEMP1, w<BR>
	skpnc<BR>
	incfsz	TEMP1, w<BR>
	addwf	ACC1, f<BR>
<BR>
; The end.<BR>
<BR>
	goto $<BR>
<BR>
 end <BR>
<BR>
<BR>
<BR>
Now, 21 * 1.8 = 37.8... So when the code generated an answer of 59, I was puzzled.  What it looks like is it generated code for a value of 2.8, not 1.8.  Since, honestly, I don't really follow this code, I am not sure how to modify it to produce 1.8.  Any help is greatly appreciated.</BLOCKQUOTE>
<!-- 39313.1049768519 EOR -->

   <LI>'



ON 20070820@12:20:58 PM at page:
http://www.piclist.com/techref/piclist/codegen/constdivmul.htm#39313.1338425926
James Newton[JMN-EFP-786] removed post 39313.1338425926

|Delete '<A TITLE="P-68.42.38.183" NAME="39313.1338425926">
</A> 
Okay, first, sorry for placing the previous question as a comment.  Secondly, I figured out what was wrong.  Normally, I begin code with a template, and that template sets the radix to decimal...<BR>
<BR>
Please feel free to delete any of this!  :)<!-- 39313.1338425926 EOR -->

   <LI>'