Q34501: word Causes "Illegal Operand Size" Warning

Article: Q34501
Product(s): See article
Version(s): 5.10   | 5.10
Operating System(s): MS-DOS | OS/2
Keyword(s): ENDUSER | | mspl13_masm
Last Modified: 12-JAN-1989

The following command causes the warning "illegal operand size:"

lds  dx, word ptr [bp+6]

However, using dword assembles clean.

The line is from the code below. The procedure foo function
receives a pointer to a string and writes it to the screen.

It accept dword and not word because the LDS assembler instruction
reads and stores a far pointer specified by the source-memory operand.
Using the word type should cause a warning with small model.
The following sample code demonstrates the problem:

 .model     medium

 .code
            PUBLIC  _foo
_foo        PROC
            push    bp
            mov     bp, sp

            lds     dx, word ptr [bp+6]    ;causes 'illegal operand size'.
                                           ;but not with use of 'dword'

            mov     ah, 40h
            mov     bx, 1
            mov     cx, 17
            int     21h

            pop     bp
            ret
_foo        ENDP
            END

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