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<h4 class="subsection">9.23.2 Syntax</h4>
<p><a name="index-g_t_0040sc_007bmit_007d-1352"></a>This syntax for the Motorola 680x0 was developed at <span class="sc">mit</span>.
<p><a name="index-M680x0-syntax-1353"></a><a name="index-syntax_002c-M680x0-1354"></a><a name="index-M680x0-size-modifiers-1355"></a><a name="index-size-modifiers_002c-M680x0-1356"></a>The 680x0 version of <code>as</code> uses instructions names and
syntax compatible with the Sun assembler. Intervening periods are
ignored; for example, ‘<samp><span class="samp">movl</span></samp>’ is equivalent to ‘<samp><span class="samp">mov.l</span></samp>’.
<p>In the following table <var>apc</var> stands for any of the address registers
(‘<samp><span class="samp">%a0</span></samp>’ through ‘<samp><span class="samp">%a7</span></samp>’), the program counter (‘<samp><span class="samp">%pc</span></samp>’), the
zero-address relative to the program counter (‘<samp><span class="samp">%zpc</span></samp>’), a suppressed
address register (‘<samp><span class="samp">%za0</span></samp>’ through ‘<samp><span class="samp">%za7</span></samp>’), or it may be omitted
entirely. The use of <var>size</var> means one of ‘<samp><span class="samp">w</span></samp>’ or ‘<samp><span class="samp">l</span></samp>’, and
it may be omitted, along with the leading colon, unless a scale is also
specified. The use of <var>scale</var> means one of ‘<samp><span class="samp">1</span></samp>’, ‘<samp><span class="samp">2</span></samp>’,
‘<samp><span class="samp">4</span></samp>’, or ‘<samp><span class="samp">8</span></samp>’, and it may always be omitted along with the
leading colon.
<p><a name="index-M680x0-addressing-modes-1357"></a><a name="index-addressing-modes_002c-M680x0-1358"></a>The following addressing modes are understood:
<dl>
<dt><dfn>Immediate</dfn><dd>‘<samp><span class="samp">#</span><var>number</var></samp>’
<br><dt><dfn>Data Register</dfn><dd>‘<samp><span class="samp">%d0</span></samp>’ through ‘<samp><span class="samp">%d7</span></samp>’
<br><dt><dfn>Address Register</dfn><dd>‘<samp><span class="samp">%a0</span></samp>’ through ‘<samp><span class="samp">%a7</span></samp>’<br>
‘<samp><span class="samp">%a7</span></samp>’ is also known as ‘<samp><span class="samp">%sp</span></samp>’, i.e., the Stack Pointer. <code>%a6</code>
is also known as ‘<samp><span class="samp">%fp</span></samp>’, the Frame Pointer.
<br><dt><dfn>Address Register Indirect</dfn><dd>‘<samp><span class="samp">%a0@</span></samp>’ through ‘<samp><span class="samp">%a7@</span></samp>’
<br><dt><dfn>Address Register Postincrement</dfn><dd>‘<samp><span class="samp">%a0@+</span></samp>’ through ‘<samp><span class="samp">%a7@+</span></samp>’
<br><dt><dfn>Address Register Predecrement</dfn><dd>‘<samp><span class="samp">%a0@-</span></samp>’ through ‘<samp><span class="samp">%a7@-</span></samp>’
<br><dt><dfn>Indirect Plus Offset</dfn><dd>‘<samp><var>apc</var><span class="samp">@(</span><var>number</var><span class="samp">)</span></samp>’
<br><dt><dfn>Index</dfn><dd>‘<samp><var>apc</var><span class="samp">@(</span><var>number</var><span class="samp">,</span><var>register</var><span class="samp">:</span><var>size</var><span class="samp">:</span><var>scale</var><span class="samp">)</span></samp>’
<p>The <var>number</var> may be omitted.
<br><dt><dfn>Postindex</dfn><dd>‘<samp><var>apc</var><span class="samp">@(</span><var>number</var><span class="samp">)@(</span><var>onumber</var><span class="samp">,</span><var>register</var><span class="samp">:</span><var>size</var><span class="samp">:</span><var>scale</var><span class="samp">)</span></samp>’
<p>The <var>onumber</var> or the <var>register</var>, but not both, may be omitted.
<br><dt><dfn>Preindex</dfn><dd>‘<samp><var>apc</var><span class="samp">@(</span><var>number</var><span class="samp">,</span><var>register</var><span class="samp">:</span><var>size</var><span class="samp">:</span><var>scale</var><span class="samp">)@(</span><var>onumber</var><span class="samp">)</span></samp>’
<p>The <var>number</var> may be omitted. Omitting the <var>register</var> produces
the Postindex addressing mode.
<br><dt><dfn>Absolute</dfn><dd>‘<samp><var>symbol</var></samp>’, or ‘<samp><var>digits</var></samp>’, optionally followed by
‘<samp><span class="samp">:b</span></samp>’, ‘<samp><span class="samp">:w</span></samp>’, or ‘<samp><span class="samp">:l</span></samp>’.
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