PIC Microcontoller Math Method

24 bit binary addition

From: Dwayne Reid

...here is an example that takes the value in R1H,M,L and adds it to the value contained in AD2H,M,L (result in AD2H,M,L). You should be able to see how to extend it to more than 24 bits.

There is a similar version that does subtraction. I often extend to 40 bits or more - its easier to do this when manipulating integer values than it is to try and figure out which bits I can discard.

;now add new sample
     movfw       R1L              ;
     addwf       AD2L,F          ;LS byte

     movfw       R1M             ;middle byte
     skpnc
       incfsz    R1M,W
         addwf   AD2M,F          ;

     movfw       R1H             ;MS byte
     skpnc
       incfsz    R1H,W
         addwf   AD2H,F          ;

Code:

• David A Cary of Motorguide Pinpoint shares this code:

  
   
  ;**********
  ;   For 17C family processors.
  ; from std.ins.aspic at http://www.embedinc.com/pic
    if fam_17
  add24    macro   dest, src, temp
           movfp   src+0, wreg
           addwf   dest+0      ;add byte 0
  
           movfp   src+1, wreg
           addwfc  dest+1      ;add byte 1
  
           movfp   src+2, wreg
           addwfc  dest+2      ;add byte 2
           endm
      endif                    ;end of 17C processor case
  ;
  
  

See also:

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