Int B3 Fn 74  - Zipkey - Convert Zipcode To Ascii Digits                   [U]

   AH = 74h
   DX = zipcode region (0-999)
   CH = last two digits of zipcode (0-99)
   ES:DI -> buffer

Return: CF set on error
       AX destroyed
   CF clear if successful
       ES:DI points one byte beyond end of digit string