stack segment para stack 'stack'
      db 128 dup(?)
stack ends
code  segment 'code'
      assume ss:stack,cs:code

start:
      mov ah,07h
      int 21h
      cmp al,7Ah
      ja  begin
      cmp al,61h
      jae zifu
      cmp al,5Bh
      ja  begin
      cmp al,41h
      ja  zifu
      cmp al,3Ah
      ja  begin
      cmp al,30h
      jae shuzi
      cmp al,20h
      jae begin
      cmp al,0Dh
      je  exit

zifu: mov dl,63h
      mov ah,02h
      int 21h
      jmp start
shuzi:mov dl,al
      mov ah,02h
      int 21h
      jmp start
begin:jmp start
exit: mov ah,4ch
      int 21h
  code ends
   end start