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<title>Using as: S12Z Register Notation</title>
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Previous: <a href="S12Z-Addressing-Modes.html#S12Z-Addressing-Modes" accesskey="p" rel="previous">S12Z Addressing Modes</a>, Up: <a href="S12Z-Syntax.html#S12Z-Syntax" accesskey="u" rel="up">S12Z Syntax</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="AS-Index.html#AS-Index" title="Index" rel="index">Index</a>]</p>
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<a name="Register-Notation"></a>
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<h4 class="subsubsection">9.24.2.3 Register Notation</h4>
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<a name="index-register-notation_002c-S12Z"></a>
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<p>Without a register prefix (see <a href="S12Z-Options.html#S12Z-Options">S12Z Options</a>), S12Z assembler code is expected in the traditional
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format like this:
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</p><div class="smallexample">
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<pre class="smallexample">lea s, (-2,s)
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st d2, (0,s)
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ld x, symbol
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tfr d2, d6
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cmp d6, #1532
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</pre></div>
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<p>However, if <code>as</code> is started with (for example) ‘<samp>-mreg-prefix=%</samp>’
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then all register names must be prefixed with ‘<samp>%</samp>’ as follows:
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</p><div class="smallexample">
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<pre class="smallexample">lea %s, (-2,%s)
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st %d2, (0,%s)
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ld %x, symbol
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tfr %d2, %d6
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cmp %d6, #1532
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</pre></div>
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<p>The register prefix feature is intended to be used by compilers
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to avoid ambiguity between symbols and register names.
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Consider the following assembler instruction:
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</p><div class="smallexample">
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<pre class="smallexample">st d0, d1
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</pre></div>
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<p>The destination operand of this instruction could either refer to the register
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‘<samp>D1</samp>’, or it could refer to the symbol named “d1”.
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If the latter is intended then <code>as</code> must be invoked with
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‘<samp>-mreg-prefix=<var>pfx</var></samp>’ and the code written as
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</p><div class="smallexample">
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<pre class="smallexample">st <var>pfx</var>d0, d1
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</pre></div>
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<p>where <var>pfx</var> is the chosen register prefix.
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For this reason, compiler back-ends should choose a register prefix which
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cannot be confused with a symbol name.
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