📄 condit.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.10 Conditional Assembly</U></STRONG>
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Conditional assembly allows to assemble or ignore selected parts of code.
This can be used to keep the code for various program variants in a single
source, to ease configuration control and maintenance. Conditional assembly
is also useful to write fancy macros.<BR>
The following fourteen meta instructions have been implemented:
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<BLOCKQUOTE>
<STRONG><PRE>
IF     &lt;expr&gt;            ELSEIF     &lt;expr&gt;
IFN    &lt;expr&gt;            ELSEIFN    &lt;expr&gt;
IFDEF  &lt;symbol&gt;          ELSEIFDEF  &lt;symbol&gt;
IFNDEF &lt;symbol&gt;          ELSEIFNDEF &lt;symbol&gt;
IFB    &lt;literal&gt;         ELSEIFB    &lt;literal&gt;
IFNB   &lt;literal&gt;         ELSEIFNB   &lt;literal&gt;
ENDIF                    ELSE
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Meta instructions overlay the Intel <NOBR>MCS-51</NOBR> assembly language, but
are not part of it! C programmers may compare them to C preprocessor commands.<BR>
In the subsequent text, IFxx is used as a collective name for the
IF/IFN/IFDEF/IFNDEF/IFB/IFNB instructions. In analogy ELSEIFxx is used as a
collective name for the ELSEIF/ELSEIFN/ELSEIFDEF/ELSEIFNDEF/ELSEIFB/ELSEIFNB
instructions (not including ELSE).
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<OL TYPE=1>
<LI><A HREF="genifxx.htm">General IFxx Construction</A></LI>
<LI><A HREF="ifxxcon.htm">IFxx and ELSEIFxx Instructions</A></LI>
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