📄 exitm.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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<STRONG><U>III.11.6 Premature End of a Macro Expansion</U></STRONG>
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<P>
Sometimes it is useful, if a macro expansion can be terminated, before
the end of the macro body is reached. This can be forced with the EXITM
(exit macro) instruction. However, this makes sense in conjunction with
conditional assembly only.
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<P>
<BR>
<STRONG>Example:</STRONG>
<BLOCKQUOTE>
<PRE>
        FLEXIBLE MACRO QUANTITY
        DB 'Text'
        IF QUANTITY LE 255
        EXITM
        ENDIF
        DW QUANTITY
        ENDM
</PRE>
The macro FLEXIBLE always has to insert the string 'Text'
into the CODE space. After that, it should insert a 16-bit
constant only, if the numerical value of the parameter
QUANTITY is greater than 255.<BR>
Otherwise the macro expansion should be terminated with
EXITM before. If the macro is called as follows,
<PRE>
        FLEXIBLE 42
</PRE>
it will be expanded to
<PRE>
        DB 'Text'
</PRE>
in list mode $GENONLY/$CONDONLY.<BR>
However, if it is called like this,
<PRE>
        FLEXIBLE 4711
</PRE>
it will be expanded to:
<PRE>
        DB 'Text'
        DW 4711
</PRE>
</BLOCKQUOTE>
</P>

<P>
When a macro expansion is terminated with EXITM, all IFxx constructions that
have been opened within the macro body so far, are closed.<BR>
Of course macro bodies may also contain control statements. If an include
file is inserted into a macro body with a $INCLUDE control, and this include
file, or a nested include file, contains an EXITM instruction, all include
file levels up to the next macro level are closed at this point, and the
expansion of that macro is terminated immediately.
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