In SX Microcontrollers, SX/B Compiler and SX-Key Tool, James Newton wrote:

[url=http://www.sxlist.com/techref/ubicom/lib/math/radix/index_sx.htm]http://www.sxlist.com/techref/ubicom/lib/math/radix/index_sx.htm [/url]
has several 8 bit to 12 bit bcd (aka half packed or packed bcd) routines... 

why 9 bits? 8 bits is easy, but:

 

2^8th is 256 which only uses about 1/3 of the capasity of a 3 digit display

2^9th is 512 so that does fit in 3 digits... gives about half the possible output values.

2^10th is 1024 which is a better fit for 3... 

 

humm.. ok, there is a 10 bit to 4 digit(?) routine (why bother with the 25 values past 999?) at

[url=http://www.sxlist.com/techref/microchip/math/radix/b2bu-10b4d-eag.htm]http://www.sxlist.com/techref/microchip/math/radix/b2bu-10b4d-eag.htm [/url]

but it hasn't been converted to parallax / SASM notation yet... that requires a few seconds at:

[url=http://www.sxlist.com/cgi-bin/mpasm2sasm2.exe]http://www.sxlist.com/cgi-bin/mpasm2sasm2.exe [/url]

which then gives us:


[code]
;======= Bin2Dec10G.asm ============= Sep 04 =========
  ;       Test of 10b binary to 4 digit conversion as
  ;       based on division by powers of 10.
  ;
  ;       E. A., Grens
  ;
  ;       For most PICs - here for 16F628 with 4 MHz
  ;       internal oscillator.
  ;
  ;       Average processor cycles for execution of
  ;       subroutine over the input range 0x000 to 0x3FF
  ;       is 88.  No variables required except the
  ;       input blh, blo and the out BCD digits.
  ;       Subroutine length 38.
  ;====================================================== 


  ;-------Set Up RAM Variables---------------------------
blo equ $20 ;lsbyte of 10b binary
bhi equ $21 ;msb
d4 equ $23 ;msdigit
d3 equ $24
d2 equ $25
d1 equ $26 ;lsd 


 ;-------Program Code-------------------------------- 

        org $00 ;Effective Reset Vector
 ;
        nop
        jmp Start ;Jump by interrupt
 ;
Start
        mov W, #$07
        mov CMCON, W ;Digital I/O
        mov W, #$03 ;Test input
        mov bhi, W
        mov W, #$FF
        mov blo, W
        mov W, #$04
        call Bin2decg
Hold
        jmp Hold ;Finished 

  

Bin2decg                      ;10b binaey to BCD
        clr d1
        clr d2
        clr d3
        clr d4
        clc
        rr bhi ;N = 4*Q + R
        rr blo ;blo = Q
        rr d1 ;d1 = R as temp, R25
        jmp B2d2 ;repeat
B2d3
        add blo, W ;get remainder
                                  ;    after /100, C = 0
        rl d1 ;*4 and add R back in
        rl blo
        rl d1
        rl blo ;4*blo + R = N -
                                  ;    1000*d4 - 100*d3
        mov W, #10
B2d4
        sub blo, W ;blo = N - 1000*d4 -
                                  ;     100*d3 - 10*d2
        sc
        jmp B2d5 ;blo10
        jmp B2d4
B2d5
        add blo, W ;put last 10 back, C=0
        mov W, blo
        mov d1, W
        ret 

        end
 
[/code]
Now, that obviously needs some polish, but it should save you some time. Note that this routine is NOT complete, it only figures out D1 by dividing blo/bhi by 10 and saving the remander, but D2 is just the same thing over again with the value left in blo/bhi after D1 is extracted. So you can stop at D3 and have your 3 digit version.

 

Please consider publishing what you come up with both here and at sxlist.com?

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