BCD4Bin:
   clr   a
   mov   r2,a
   mov   r3,a
   mov   r4,a
   mov   r5,a
   call  BCD1BinPlus
   call  BCD1BinPlus
   call  BCD1BinPlus
;   call  BCD1BinPlus ;fallthrough
;   ret

BCD1BinPlus:   ;converts BCD in @R0 into bin in ACC; uses no extra resources
   mov   a,@r0
   inc   r0
   xrl   a,#0F0h     ; With or without ... :-)
   jbc   acc.4,BCD1BX1
   add   a,#10
BCD1BX1:
   jbc   acc.5,BCD1BX2
   add   a,#20

   .......