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<title>Z80 Opcodes - Using as</title>
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<link rel="up" href="Z80_002dDependent.html#Z80_002dDependent" title="Z80-Dependent">
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This file documents the GNU Assembler "as".
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Copyright (C) 1991-2015 Free Software Foundation, Inc.
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<a name="Z80-Opcodes"></a>
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<p>
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Previous: <a rel="previous" accesskey="p" href="Z80-Directives.html#Z80-Directives">Z80 Directives</a>,
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Up: <a rel="up" accesskey="u" href="Z80_002dDependent.html#Z80_002dDependent">Z80-Dependent</a>
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<h4 class="subsection">9.53.5 Opcodes</h4>
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<p>In line with common practice, Z80 mnemonics are used for both the Z80 and
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the R800.
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<p>In many instructions it is possible to use one of the half index
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registers (‘<samp><span class="samp">ixl</span></samp>’,‘<samp><span class="samp">ixh</span></samp>’,‘<samp><span class="samp">iyl</span></samp>’,‘<samp><span class="samp">iyh</span></samp>’) in stead of an
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8-bit general purpose register. This yields instructions that are
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documented on the R800 and undocumented on the Z80.
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Similarly <code>in f,(c)</code> is documented on the R800 and undocumented on
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the Z80.
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<p>The assembler also supports the following undocumented Z80-instructions,
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that have not been adopted in the R800 instruction set:
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<dl>
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<dt><code>out (c),0</code><dd>Sends zero to the port pointed to by register c.
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<br><dt><code>sli </code><var>m</var><dd>Equivalent to <var>m</var><code> = (</code><var>m</var><code><<1)+1</code>, the operand <var>m</var> can
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be any operand that is valid for ‘<samp><span class="samp">sla</span></samp>’. One can use ‘<samp><span class="samp">sll</span></samp>’ as a
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synonym for ‘<samp><span class="samp">sli</span></samp>’.
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<br><dt><var>op</var><code> (ix+</code><var>d</var><code>), </code><var>r</var><dd>This is equivalent to
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<pre class="example"> ld <var>r</var>, (ix+<var>d</var>)
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<var>opc</var> <var>r</var>
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ld (ix+<var>d</var>), <var>r</var>
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</pre>
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<p>The operation ‘<samp><var>opc</var></samp>’ may be any of ‘<samp><span class="samp">res </span><var>b</var><span class="samp">,</span></samp>’,
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‘<samp><span class="samp">set </span><var>b</var><span class="samp">,</span></samp>’, ‘<samp><span class="samp">rl</span></samp>’, ‘<samp><span class="samp">rlc</span></samp>’, ‘<samp><span class="samp">rr</span></samp>’, ‘<samp><span class="samp">rrc</span></samp>’,
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‘<samp><span class="samp">sla</span></samp>’, ‘<samp><span class="samp">sli</span></samp>’, ‘<samp><span class="samp">sra</span></samp>’ and ‘<samp><span class="samp">srl</span></samp>’, and the register
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‘<samp><var>r</var></samp>’ may be any of ‘<samp><span class="samp">a</span></samp>’, ‘<samp><span class="samp">b</span></samp>’, ‘<samp><span class="samp">c</span></samp>’, ‘<samp><span class="samp">d</span></samp>’,
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‘<samp><span class="samp">e</span></samp>’, ‘<samp><span class="samp">h</span></samp>’ and ‘<samp><span class="samp">l</span></samp>’.
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<br><dt><var>opc</var><code> (iy+</code><var>d</var><code>), </code><var>r</var><dd>As above, but with ‘<samp><span class="samp">iy</span></samp>’ instead of ‘<samp><span class="samp">ix</span></samp>’.
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</dl>
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<p>The web site at <a href="http://www.z80.info">http://www.z80.info</a> is a good starting place to
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find more information on programming the Z80.
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