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115 lines
4.3 KiB
HTML
115 lines
4.3 KiB
HTML
15 years ago
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<title>AVR-Modifiers - Using as</title>
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<link title="Top" rel="start" href="index.html#Top">
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<link rel="up" href="AVR-Syntax.html#AVR-Syntax" title="AVR Syntax">
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<link rel="prev" href="AVR_002dRegs.html#AVR_002dRegs" title="AVR-Regs">
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<link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage">
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<!--
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This file documents the GNU Assembler "as".
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Copyright (C) 1991, 92, 93, 94, 95, 96, 97, 98, 99, 2000, 2001, 2002,
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2006, 2007 Free Software Foundation, Inc.
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Permission is granted to copy, distribute and/or modify this document
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under the terms of the GNU Free Documentation License, Version 1.1
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or any later version published by the Free Software Foundation;
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with no Invariant Sections, with no Front-Cover Texts, and with no
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Back-Cover Texts. A copy of the license is included in the
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section entitled ``GNU Free Documentation License''.
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</head>
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<body>
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<div class="node">
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<p>
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<a name="AVR_002dModifiers"></a>Previous: <a rel="previous" accesskey="p" href="AVR_002dRegs.html#AVR_002dRegs">AVR-Regs</a>,
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Up: <a rel="up" accesskey="u" href="AVR-Syntax.html#AVR-Syntax">AVR Syntax</a>
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<hr><br>
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</div>
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<h5 class="subsubsection">9.4.2.3 Relocatable Expression Modifiers</h5>
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<p><a name="index-AVR-modifiers-654"></a><a name="index-syntax_002c-AVR-655"></a>
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The assembler supports several modifiers when using relocatable addresses
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in AVR instruction operands. The general syntax is the following:
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<pre class="smallexample"> modifier(relocatable-expression)
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</pre>
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<a name="index-symbol-modifiers-656"></a>
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<dl>
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<dt><code>lo8</code><dd>
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This modifier allows you to use bits 0 through 7 of
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an address expression as 8 bit relocatable expression.
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<br><dt><code>hi8</code><dd>
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This modifier allows you to use bits 7 through 15 of an address expression
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as 8 bit relocatable expression. This is useful with, for example, the
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AVR <span class="samp">ldi</span> instruction and <span class="samp">lo8</span> modifier.
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<p>For example
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<pre class="smallexample"> ldi r26, lo8(sym+10)
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ldi r27, hi8(sym+10)
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</pre>
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<br><dt><code>hh8</code><dd>
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This modifier allows you to use bits 16 through 23 of
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an address expression as 8 bit relocatable expression.
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Also, can be useful for loading 32 bit constants.
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<br><dt><code>hlo8</code><dd>
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Synonym of <span class="samp">hh8</span>.
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<br><dt><code>hhi8</code><dd>
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This modifier allows you to use bits 24 through 31 of
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an expression as 8 bit expression. This is useful with, for example, the
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AVR <span class="samp">ldi</span> instruction and <span class="samp">lo8</span>, <span class="samp">hi8</span>, <span class="samp">hlo8</span>,
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<span class="samp">hhi8</span>, modifier.
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<p>For example
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<pre class="smallexample"> ldi r26, lo8(285774925)
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ldi r27, hi8(285774925)
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ldi r28, hlo8(285774925)
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ldi r29, hhi8(285774925)
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; r29,r28,r27,r26 = 285774925
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</pre>
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<br><dt><code>pm_lo8</code><dd>
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This modifier allows you to use bits 0 through 7 of
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an address expression as 8 bit relocatable expression.
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This modifier useful for addressing data or code from
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Flash/Program memory. The using of <span class="samp">pm_lo8</span> similar
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to <span class="samp">lo8</span>.
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<br><dt><code>pm_hi8</code><dd>
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This modifier allows you to use bits 8 through 15 of
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an address expression as 8 bit relocatable expression.
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This modifier useful for addressing data or code from
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Flash/Program memory.
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<br><dt><code>pm_hh8</code><dd>
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This modifier allows you to use bits 15 through 23 of
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an address expression as 8 bit relocatable expression.
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This modifier useful for addressing data or code from
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Flash/Program memory.
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</dl>
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</body></html>
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