%macro    UpCase 2                 ; Target,Length 
          mov CX,%2                ; CX is acting as length counter for loop
          mov BX,%1                ; String will be at DS:BX
%%Tester: cmp BYTE [BX],'a'        ; Is string character below 'a'?
          jb %%Bump                ; If so, leave character alone
          cmp BYTE [BX],'z'        ; Is string character above 'z'?
          ja %%Bump                ; If so, leave character alone
          and BYTE [BX],11011111b  ; Char is lc alpha, so force bit 5 to 0
%%Bump:   inc BX                   ; Bump BX to point to next char in string
          loop %%Tester            ; And go back and do it again!
%endmacro