📄 operator.htm

📁 一份51的编译程序,dos版本的. 英文名字MCS-51 Microcontroller Family Macro Assembler
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<P>
<STRONG><U>III.11.5 Macro Operators</U></STRONG>
</P>

<P>
There are some special control characters, which are very useful for macro
definition, call and expansion:
</P>

<P>
<TABLE BORDER CELLPADDING=8>
<TR><TD ALIGN=CENTER NOWRAP><BIG>;;</BIG></TD>
    <TD NOWRAP><STRONG>Macro commentary</STRONG></TD>
    <TD>Normally, comments in body lines are also contained in the expanded
        lines. If a commentary begins with ';;' however, it is not stored
        during macro definition. Therefore, it doesn't consume memory space,
        and appears in the list file in the macro definition only, but not
        in the expanded lines.</TD>
</TR>
<TR><TD ALIGN=CENTER NOWRAP><BIG>!</BIG></TD>
    <TD NOWRAP><STRONG>Literal operator</STRONG></TD>
    <TD>If the escape character '!' precedes another printable character in
        a macro argument, the assembler is forced to treat that character
        literally. This means it will be passed to the macro, even if it is
        a control character, while the literal operator itself is removed.</TD>
</TR>
<TR><TD ALIGN=CENTER NOWRAP><BIG>&lt;&nbsp;&gt;</BIG></TD>
    <TD NOWRAP><STRONG>Literal brackets</STRONG></TD>
    <TD>If a macro argument is intended to contain separation or control
        characters, it must be enclosed in literal brackets &lt; ... &gt; to pass
        it to the macro as one argument string, while the outermost pair of
        brackets is removed. Literal brackets can be nested to any depth.</TD>
</TR>
<TR><TD ALIGN=CENTER NOWRAP><BIG>%</BIG></TD>
    <TD NOWRAP><STRONG>Evaluation</STRONG></TD>
    <TD>If a macro argument is preceded by the evaluation operator '%', it
        is interpreted as an expression, which will be evaluated before it
        is passed to the macro. The actual argument string will not be the
        expression itself, but a decimal ASCII representation of its value.
        The expression must be known on <NOBR>pass 1</NOBR>.</TD>
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<TR><TD ALIGN=CENTER NOWRAP><BIG>&amp;</BIG></TD>
    <TD NOWRAP><STRONG>Substitution</STRONG></TD>
    <TD>The '&amp;' character separates parameter names (local symbols) from
        surrounding text. Outside quoted strings and commentary it serves
        only as a general separation character. This applies always when
        a local symbol directly precedes or follows another alphanumeric
        string. Inside quoted strings and commentary, a local symbol must
        be preceded by '&amp;' if it is to be substituted there.<BR>
        During every macro expansion, the assembler removes exactly one '&amp;'
        from every sequence of '&amp;' characters. This allows for example, to
        define a nested macro inside a macro body, which also uses the
        substitution operator '&amp;': one writes simply '&amp;&amp;'!</TD>
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<P>
<BR>
<STRONG>Example 1:</STRONG>
<BLOCKQUOTE>
The commentary should only be visible in the definition
of the macro LICENSE:
<PRE>
        LICENSE MACRO
        DB 'Copyright'  ;;legal stuff
        ENDM
</PRE>
When called, the expanded macro body is looking
like this in the list file:
<PRE>
        DB 'Copyright'
</PRE>
</BLOCKQUOTE>
</P>

<P>
<BR>
<STRONG>Example 2:</STRONG>
<BLOCKQUOTE>
<PRE>
        SPECIAL !;
</PRE>
passes a semicolon to the macro SPECIAL as a literal
argument. This could also be done with
<PRE>
        SPECIAL &lt;;&gt;
</PRE>
</BLOCKQUOTE>
</P>

<P>
<BR>
<STRONG>Example 3:</STRONG>
<BLOCKQUOTE>
The macro CONST defines a 16-bit constant in ROM:
<PRE>
        CONST MACRO NUMB
        DW NUMB
        ENDM
</PRE>
If it is called as shown below,
<PRE>
        CONST 0815H+4711-42
</PRE>
the parameter NUMB would be substituted as follows:
<PRE>
        DW 0815H+4711-42
</PRE>
If the same macro argument is preceded by a '%' however,
<PRE>
        CONST %0815H+4711-42
</PRE>
the substitution will result in:
<PRE>
        DW 6738
</PRE>
</BLOCKQUOTE>
</P>

<P>
<BR>
<STRONG>Example 4:</STRONG>
<BLOCKQUOTE>
During substitution, both arguments of the macro CONCAT
should form a seamless symbol name:
<PRE>
        CONCAT MACRO NAM, NUM
        MOV R3,#0
NAM&amp;NUM: DJNZ R3,NAM&amp;NUM
        ENDM
</PRE>
When CONCAT is called as follows,
<PRE>
        CONCAT LABEL, 08
</PRE>
the parameters NAM and NUM are substituted during macro
expansion as shown below:
<PRE>
        MOV R3,#0
LABEL08: DJNZ R3,LABEL08
</PRE>
</BLOCKQUOTE>
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