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

According to
[url=http://www.sxlist.com/techref/ubicom/lib/math/sub/bcdp2_sx.htm]http://www.sxlist.com/techref/ubicom/lib/math/sub/bcdp2_sx.htm[/url] 

the following should also work (I removed the carry restore instructions as they are not needed)


[code]
'calculate x-y where x and y are packed bcd values
'use val = sub_bcd x,y
FUNC sub_bcd
asm
  mov W,__PARAM2 ;__PARAM1 = __PARAM1 - __PARAM2
  sub __PARAM1,W
  clr W
  sb DC          ;if lsn of __PARAM1 < lsn of __PARAM2 (dec)
  or W,#$06      ;then substract extra 6
  sb C           ;Similarly for the msn
  or W, #$60
  sub __PARAM1,W ;correct result
endasm
  RETURN __PARAM1
ENDFUNC
 
[/code]
Notice that this calculates the more general x-y rather than x-1 

regards peter

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