PIC Microcontoller Radix Math Method

BCD packed to binary 2 digit to 8 bit

From: Scott Dattalo

         rrf   bcd, W 
        andlw 01111000b  ;W = tens*8 
        movwf temp 
        clrc 
        rrf   temp, F    ;temp = tens*4 
        rrf   temp, F    ;temp = tens*2 
        subwf bcd, W     ;W = tens*16 + ones - tens*8 
                         ;W = tens*8 + ones 
        addwf temp, W    ;W = tens*10 + ones 

Code:

• Silvan Minghetti shares this code:

  ; ==========================================================
  ; From: Scott Dattalo
  ;
  ; This version saves one cycle.
  ;
          swapf   bcd, W
          andlw   0x0F            ; W=tens
          movwf   temp
          addwf   temp, W         ; W=2*tens
          addwf   temp, F         ; temp=3*tens (note carry is cleared)
          rlf     temp, W         ; W=6*tens
          subwf   bcd, W          ; W = 16*tens+ones - 6*tens
  
  
  ; ==========================================================
  ; From: Silvan Minghetti
  ;
  ; Does not require an additional temp register, but trashes
  ; the content of the bcd register.
  ;
  ; Expects bcd value in 'bcd', returns binary value in WREG.
  ; To return the binary value in 'bcd', change the last line
  ; to subwf bcd, F
  ;
          swapf   bcd, F
          rlf     bcd, W
          andlw   b'00011110'     ; WREG = tens * 2
          swapf   bcd, F
  
          subwf   bcd, F          ; bcd  = (tens * 16) - (tens * 2) + ones
          subwf   bcd, F          ; bcd  = (tens * 14) - (tens * 2) + ones
          subwf   bcd, W          ; WREG = (tens * 12) - (tens * 2) + ones
  
  
  ; ==========================================================
  ; From: Scott Dattalo
  ;
  ; The upper method adapted for the PIC18 Family, saves one
  ; more cycle.
  ;
          swapf   bcd, W
          andlw   0x0F            ; W= tens
          rlncf   WREG, W         ; W= 2*tens
          subwf   bcd, F          ; 16*tens + ones - 2*tens
          subwf   bcd, F          ; 14*tens + ones - 2*tens
          subwf   bcd, W          ; 12*tens + ones - 2*tens
  

Comments:

• ; For PIC16 with enhanced istruction set. 8 cycles, uses only W
  
  btfsc WREG, 4
  addlw D'10' - H'10'
  btfsc WREG, 5
  addlw D'20' - H'20'
  btfsc WREG, 6
  addlw D'40' - H'40'
  btfsc WREG, 7
  addlw D'80' - H'80'
  
• yesiamwds-netscape-Q5A says Here is another 6 instruction routine for P18:
  ; ========================================================
  ; by Warren Schroeder
  

  RRCF         BCD, W          ; BCD/2 in WREG
  RRCF         WREG, W       ; BCD/2/2 in WREG
  ANDLW     0x3C               ; mask upper nibble as 4 * tens
  SUBWF      BCD, F           ; BCD = (16 * tens) - (4 * tens) = 12 * tens + ones
  RRNCF      WREG, W       ; BCD/2/2/2 in WREG = (2 * tens)
  SUBWF      BCD, F           ; BCD = (12 * tens) - (2 * tens) = 10 * tens + ones

Tomas Kocian Says:

Another method, using 6 cycles without additional registers:
swapf bcd,w ;separate tenths
andlw 0F
mullw 0A ;multiply by 10
movf bcd,w
andlw 0F ;separate below 10
addwf PRODL,w ;add to multiply result