please dont rip this site
;*******************************************************************
;scale_hex2dec
;  The purpose of this routine is to scale a hexadecimal byte to a
;decimal byte. In other words, if 'h' is a hexadecimal byte then
;the scaled decimal equivalent 'd' is:
;    d = h * 100/256.
;Note that this can be simplified:
;    d = h * 25 / 64 = h * 0x19 / 0x40
;Multiplication and division can be expressed in terms of shift lefts
;and shift rights:
;    d = [ (h<<4) + (h<<3) + h ] >> 6
;The program divides the shifting as follows so that carries are
automatically
;taken care of:
;    d =   (h + (h + (h>>3)) >> 1) >> 2
;
;Inputs:   W - should contain 'h', the hexadecimal value to be scaled
;Outputs:  W - The scaled hexadecimal value is returned in W
;Memory:   temp
;Calls:    none
scale_hex2dec
        MOVWF   temp            ;Hex value is in W.
        CLRC                    ;Clear the Carry bit so it doesn't affect
RRF
        RRF     temp,F
        CLRC
        RRF     temp,F
        CLRC
        RRF     temp,F          ;temp = h>>3
        ADDWF   temp,F          ;temp = h + (h>>3)
        RRF     temp,F          ;temp = (h + (h>>3)) >> 1
        ADDWF   temp,F          ;temp = h + ((h + (h>>3)) >> 1)
        RRF     temp,F
        CLRC
        RRF     temp,W          ;d = W = (h + (h + (h>>3)) >> 1) >> 2
        RETURN

For the more general case:

 C = A*B/255

There is another trick that you can attempt. Recall the power series for division:

   N        N    /     / e \   / e \2  / e \3      \
-------  = --- * | 1 - |---| + |---| - |---| + ... |
 v + e      v    \     \ v /   \ v /   \ v /       /

If, N=A*B, v+e = 255. If you let v=256 and e=-1 then the series simplifies to:

   A*B      A*B    /    / 1 \   / 1 \2  / 1 \3      \
--------  = --- * | 1 + |---| + |---| + |---| + ... |
 256 - 1    256    \    \256/   \256/   \256/       /

Or just keeping the first two terms:

   A*B       A*B    /     1  \
--------  ~= --- * | 1 + --- |
   255       256    \    256 /

If A & B are 8-bit quantites, then the second term in the series would produce 0 (you'd be dividing the product A*B by 256 twice). However, as Harold notes, you may use the second term to round the result. Specifically, if you treated the multiplication (conceptually) as floating point then you'll end up with a fractional component that's greater than 0.5 if A*B is greater than 2^15. Or stated differently, if the most significant bit is set in the product, then increment the result.


file: /Techref/microchip/scale.htm, 2KB, , updated: 1999/9/28 17:29, local time: 2024/3/28 10:24,
TOP NEW HELP FIND: 
34.230.68.214:LOG IN

 ©2024 These pages are served without commercial sponsorship. (No popup ads, etc...).Bandwidth abuse increases hosting cost forcing sponsorship or shutdown. This server aggressively defends against automated copying for any reason including offline viewing, duplication, etc... Please respect this requirement and DO NOT RIP THIS SITE. Questions?
Please DO link to this page! Digg it! / MAKE!

<A HREF="http://piclist.com/Techref/microchip/scale.htm"> microchip scale</A>

After you find an appropriate page, you are invited to your to this massmind site! (posts will be visible only to you before review) Just type a nice message (short messages are blocked as spam) in the box and press the Post button. (HTML welcomed, but not the <A tag: Instead, use the link box to link to another page. A tutorial is available Members can login to post directly, become page editors, and be credited for their posts.


Link? Put it here: 
if you want a response, please enter your email address: 
Attn spammers: All posts are reviewed before being made visible to anyone other than the poster.
Did you find what you needed?

  PICList 2024 contributors:
o List host: MIT, Site host massmind.org, Top posters @none found
- Page Editors: James Newton, David Cary, and YOU!
* Roman Black of Black Robotics donates from sales of Linistep stepper controller kits.
* Ashley Roll of Digital Nemesis donates from sales of RCL-1 RS232 to TTL converters.
* Monthly Subscribers: Gregg Rew. on-going support is MOST appreciated!
* Contributors: Richard Seriani, Sr.
 

Welcome to piclist.com!

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

  .