mov    dph,a   ;instead of push - sparing stack space and a bit of code/speed too
   mov    a,vecr
   add    a,#LOW(positionx)
   mov    dpl,a
   clr    a
   addc   a,#HIGH(positionx)
   xch    a,dph  ;this restores acc, too
   movx   @dptr,a