VMS Help MACRO, VAX MACRO Assembler, Directives, .NTYPE  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    Determines the addressing mode of the specified operand.

      .NTYPE symbol,operand

    symbol

    Any legal VAX MACRO symbol.  This symbol is assigned a value equal
    to the  8-  or  16-bit  addressing  mode  of  the  operand argument
    that follows.

    operand

    Any legal address expression, as you use it with an  opcode.   If
    no argument is specified, 0 is assumed.

    The value of the symbol is set to the specified addressing mode.
    In most  cases,  an  8-bit (1-byte) value is returned.  Bits 0
    through 3 specify the register associated with the mode, and bits 4
    through  7 specify  the  addressing  mode.   Literal mode is
    indicated by a 0 in bits 4 through 7,  instead  of  the  values  0
    through  3.   Mode  1 indicates  an  immediate  mode  operand, mode
    2 indicates an absolute mode operand, and mode 3 indicates a
    general mode operand.

    For indexed addressing mode, a 16-bit  (2-byte)  value  is
    returned. The  high-order byte contains the addressing mode of the
    base operand specifier and the low-order byte contains the
    addressing mode of  the primary operand (the index register).