The operand field can contain operands for instructions or
    arguments for either assembler directives or macro calls.

    Operands for instructions identify the memory locations or the
    registers that are used by the machine operation. The operand
    field for a specific instruction must contain the correct number
    and type of operands required by that instruction.

    Arguments for a directive must meet the format requirements of
    that directive.

    Operands for a macro must meet the requirements specified in the
    macro definition.

    Use a comma (,)  to separate operands for instructions and
    directives.

    The semicolon that starts the comment field terminates the
    operand field. If a line does not have a comment field, the
    operand field is terminated by the end of the line.

    In the following source statement example, 50 is the operand
    field supplied to the operator field, .BLKL:

    EXP:    .BLKL   50          ; Table stores expected values