... so it's expected you "speak" at least a little bit the '51 asm:

DecAscii2Bin:
   mov   dptr,#ascii
   clr   a
   mov   r2,a
   mov   r3,a
   mov   r4,a
   mov   r5,a
DA2BLoop:
   clr   a 
   movc  a,@a+dptr
   jz    DA2BEnd
   add   a,#-'0'
   xch   a,r2
   mov   b,#10
   mul   ab
   add   a,r2
   mov   r2,a
   mov   a,b
   addc  a,#0
   xch   a,r3
   mov   b,#10
   mul   ab
   add   a,r3
   mov   r3,a
   mov   a,b
   addc  a,#0
   xch   a,r4
   mov   b,#10
   mul   ab
   add   a,r4
   mov   r4,a
   mov   a,b
   addc  a,#0
   xch   a,r5
   mov   b,#10
   mul   ab
   add   a,r5
   mov   r5,a
   inc   dptr
   jmp   DA2BLoop
DA2BEnd:
   ret

ascii: db '1234567890',0

   end

I doubt it will help too much, though...

JW