244 lines
14 KiB
HTML
244 lines
14 KiB
HTML
<?xml version="1.0" encoding="utf-8"?>
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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
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<html xmlns:MadCap="http://www.madcapsoftware.com/Schemas/MadCap.xsd" MadCap:lastBlockDepth="6" MadCap:lastHeight="94" MadCap:lastWidth="853" MadCap:disableMasterStylesheet="true" MadCap:tocPath="" MadCap:InPreviewMode="false" MadCap:PreloadImages="false" MadCap:RuntimeFileType="Topic" MadCap:TargetType="WebHelp" lang="en-us" xml:lang="en-us" MadCap:PathToHelpSystem="../../../" MadCap:HelpSystemFileName="Default.xml" MadCap:SearchType="Stem">
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<head><title>WRITE</title>
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<link href="../../SkinSupport/MadCap.css" rel="stylesheet" />
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<link href="../../Resources/Stylesheets/BSE_Help.css" rel="stylesheet" />
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<script src="../../SkinSupport/MadCapAll.js" type="text/javascript">
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</script>
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</head>
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<body>
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<h1 class="code">WRITE</h1>
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<div class="ImagePlusCaption">
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<div class="Col2">
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<p>
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<img src="../../graphics/pgm_icon1.gif" border="0" alt="BS1 icon" title="BS1 icon" />
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<img src="../../graphics/pgm_icon2.gif" border="0" alt="BS2 icon" title="BS2 icon" />
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<img src="../../graphics/pgm_icon2e.gif" border="0" alt="BS2e icon" title="BS2e icon" />
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<img src="../../graphics/pgm_icon2sx.gif" border="0" alt="BS2sx icon" title="BS2sx icon" />
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<img src="../../graphics/pgm_icon2p.gif" border="0" alt="BS2p icon" title="BS2p icon" />
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<img src="../../graphics/pgm_icon2pe.gif" border="0" alt="BS2pe icon" title="BS2pe icon" />
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<img src="../../graphics/pgm_icon2px.gif" border="0" alt="BS2px icon" title="BS2px icon" /><span class="code_in_text"> {PBASIC 2.5}</span>
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</p>
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</div>
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<p style="text-align: right;"><a href="../ExampleTopics/WriteEx.htm" target="" title="" alt="" class="MCXref_0">WRITE Examples</a>
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</p>
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<p> </p>
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</div>
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<p class="clear"> </p>
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<p> </p>
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<p class="PlainText">Syntax <img align="absmiddle" src="../../graphics/mini_1.gif" />:
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<span class="keyword_in_text">WRITE</span> <![CDATA[ ]]><i>Location</i>,<i><![CDATA[ ]]>Value</i><br />Syntax <img align="absmiddle" src="../../graphics/mini_2_inline.gif" />:
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<span class="keyword_in_text">WRITE</span> <![CDATA[ ]]><i>Location, </i>{Word}<i><![CDATA[ ]]>Value <![CDATA[ ]]></i>{, {Word}<i><![CDATA[ ]]>Value ...</i>}</p>
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<h2>Function</h2>
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<p class="PlainText">Write <i>Value</i> into <i>Location</i> in EEPROM. On the BS2 family, multiple
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<i>Value</i> may be written to consecutive locations.‡
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</p>
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<ul>
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<li value="1"><b><i>Location</i></b> is a variable/constant/expression* (0 - 255 on BS1,
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0 - 2047 on all other BASIC Stamp modules) that specifies the EEPROM address to
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write to.</li>
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<li value="2"><b><i>Value</i></b> is a variable/constant/expression* (0 - 255, or 0 - 65535 if using the optional Word modifier‡) specifying the
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value to be stored. </li>
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</ul>
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<p class="PlainText">*<img src="../../graphics/bs1note.gif" style="vertical-align: super;" /> Note: expressions are not allowed as arguments on the BS1.</p>
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<p class="PlainText">‡Note: The optional arguments require PBASIC 2.5.</p>
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<h2>Quick Facts</h2>
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<table width="100%" cellpadding="4" cellspacing="0" border="1">
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<col />
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<col style="width: 214px;" />
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<col />
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<col />
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<col />
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<tr>
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<td width="16%" align="center" bgcolor="#CFCFCF"> </td>
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<td align="center" bgcolor="#CFCFCF">BS1</td>
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<td width="21%" align="center" bgcolor="#CFCFCF">BS2</td>
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<td width="21%" align="center" bgcolor="#CFCFCF">BS2e and BS2sx</td>
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<td width="21%" align="center" bgcolor="#CFCFCF">BS2p, BS2pe, and BS2px</td>
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</tr>
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<tr>
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<td align="center" bgcolor="#CFCFCF">Range of EEPROM locations</td>
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<td align="center">0 to 255</td>
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<td align="center">0 to 2047</td>
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<td align="center">0 to 2047</td>
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<td align="center">0 to 2047<br></br>(see notes below)</td>
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</tr>
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<tr>
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<td align="center" bgcolor="#CFCFCF">Maximum number of writes per location</td>
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<td align="center">10 million</td>
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<td align="center">10 million</td>
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<td align="center">100,000</td>
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<td align="center">100,000</td>
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</tr>
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<tr>
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<td align="center" bgcolor="#CFCFCF">Special Notes</td>
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<td align="center">N/A</td>
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<td align="center">N/A</td>
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<td align="center"><span class="keyword_in_text">WRITE</span> only works with current program slot on BS2e
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and BS2sx.</td>
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<td align="center"><span class="keyword_in_text">WRITE</span> works with any program slot as set by the
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<span class="keyword_in_text">STORE</span> command.</td>
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</tr>
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<tr>
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<td align="center" bgcolor="#CFCFCF">Related Commands</td>
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<td align="center" colspan="1">
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<p colspan="1" align="center"><a href="READ.htm" target="" title="" alt="" class="MCXref_0">READ</a>, <a href="EEPROM.htm" target="" title="" alt="" class="MCXref_0">EEPROM</a></p>
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</td>
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<td align="center" colspan="2">
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<p colspan="2" align="center"><a href="READ.htm" target="" title="" alt="" class="MCXref_0">READ</a>, <a href="DATA.htm" target="" title="" alt="" class="MCXref_0">DATA</a></p>
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</td>
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<td align="center" colspan="1">
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<p colspan="1" align="center"><a href="READ.htm" target="" title="" alt="" class="MCXref_0">READ</a>, <a href="DATA.htm" target="" title="" alt="" class="MCXref_0">DATA</a>, <a href="STORE.htm" target="" title="" alt="" class="MCXref_0">STORE</a></p>
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</td>
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</tr>
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<tr>
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<td align="center" bgcolor="#CFCFCF">PBASIC 2.5 Syntax Options</td>
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<td align="center">n/a</td>
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<td align="center" colspan="3">Multiple sequential variables may be writtten to the Scratch Pad RAM, and the optional WORD modifier may be specified to store 16-bit values.</td>
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</tr>
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</table>
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<h2>Explanation</h2>
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<p class="PlainText">The EEPROM is used for both program storage (which builds downward from address
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255 on BS1, 2047 on all other BASIC Stamp models) and data storage (which builds upward
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from address 0). The <span class="keyword_in_text">WRITE</span> instruction stores a value to any EEPROM
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address. Any location within the EEPROM can be written to (including your PBASIC
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program's locations) at run-time. This feature is mainly used to store long-term
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data to EEPROM; data stored in EEPROM is not lost when the power is removed.</p>
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<p class="PlainText">The following <span class="keyword_in_text">WRITE</span> command stores the value 245 at location 100:</p><pre class="BScode" xml:space="preserve">
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WRITE 100, 245
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</pre>
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<p class="PlainText">The EEPROM is organized as a sequential set of byte-sized memory locations.
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With the BS1, the <span class="keyword_in_text">WRITE</span> instruction only stores byte-sized values into
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EEPROM. This does not mean that you can't write word-sized values, however.
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A word consists of two bytes, called a low-byte and a high-byte. If you wanted
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to write a word-sized value, you'll need to use two <span class="keyword_in_text">WRITE</span> commands and a
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word-size value or variable (along with some handy modifiers). For example:</p>
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<p>
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<img src="../../graphics/bs1_inline.gif" border="0">
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</img>
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</p><pre class="BScode" xml:space="preserve">
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SYMBOL value = W1 ' word-sized variable
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SYMBOL valLo = B2 ' B2 is the low-byte of W1
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SYMBOL valHi = B3 ' B3 is the high-byte of W1
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Main:
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value = 1125
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WRITE 0, valLo
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WRITE 1, valHi
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END
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</pre>
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<p>
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<img src="../../graphics/bs2all_inline.gif" border="0">
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</img>
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</p><pre class="BScode" xml:space="preserve">
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value VAR Word
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Main:
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value = 1125
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WRITE 0, value.LowByte
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WRITE 1, value.HighByte
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END
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</pre>
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<p class="PlainText">When this program runs, the two <span class="keyword_in_text">WRITE</span> commands will store the low-byte
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and high-byte of the number 1125 into EEPROM.</p>
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<p class="PlainText">With the BS2 family, the Word modifier can be used to write 16-bit values.
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The low byte of the value will be written to <i>Location</i>, the high byte will
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be written to <i>Location + 1</i> (<i>"Little Endian"</i> ).</p>
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<p>
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<img src="../../graphics/bs2all_inline.gif" border="0">
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</img>
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</p><pre class="BScode" xml:space="preserve">
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' {$PBASIC 2.5}
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value VAR Word
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value2 VAR Word
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addr VAR Word ' EEPROM address
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test VAR Byte ' test byte read back
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Main:
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value = $1125
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value2 = $2003
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WRITE 0, Word value, Word value2 ' write value at locations 0 & 1
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' and value2 at locations 2 & 3
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FOR addr = 0 TO 3 ' display "25 11 03 20"
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READ addr, test
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DEBUG HEX2 test, " "
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NEXT
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END
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</pre>
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<p class="PlainText">EEPROM differs from RAM, the memory in which variables are stored, in several
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respects: </p>
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<ol>
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<li value="1">Writing to EEPROM takes more time than storing a value in a variable.
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Depending on many factors, it may take several milliseconds for the EEPROM to
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complete a write. RAM storage is nearly instantaneous. </li>
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<li value="2">The EEPROM can only accept a finite number of write cycles per location
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before it wears out. The table above indicates the guaranteed number of writes
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before failure. If a program frequently writes to the same EEPROM location,
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it makes sense to estimate how long it might take to exceed the guaranteed
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maximum. For example, on the BS2, at one write per second (86,400 writes/day)
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it would take nearly 116 days of continuous operation to exceed 10 million. </li>
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<li value="3">The primary function of the EEPROM is to store programs (data is stored in
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leftover space). If data overwrites a portion of your program, the program
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will most likely crash. </li>
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</ol>
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<p class="PlainText">Check the program's memory map to determine what portion of memory your program
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occupies and make sure that EEPROM writes cannot stray into this area. You may also
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use the DATA directive on the BS2, BS2e, BS2sx, BS2p, and BS2pe to set aside EEPROM
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space. </p>
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<p>
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<img src="../../graphics/bs1_inline.gif" border="0">
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</img>
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</p>
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<p class="PlainText">On the BS1, location 255 holds the address of the last instruction in your
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program. Therefore, your program can use any space below the address given in
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location 255. For example, if location 255 holds the value 100, then your program
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can use locations 0-99 for data.</p>
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<p>
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<img src="../../graphics/bs2all_inline.gif" border="0">
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</img>
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</p>
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<p class="PlainText">On other BASIC Stamp models, you'll need to view the Memory Map of the program before
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you download it, to determine the last EEPROM location used. </p>
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<p>
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<img src="../../graphics/bs2ppepx_inline.gif" border="0">
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</img>
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</p>
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<p class="PlainText">On the BS2p, BS2pe and BS2px the <span class="keyword_in_text">READ</span> and <span class="keyword_in_text">WRITE</span> commands can
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affect locations in any program slot as set by the <span class="keyword_in_text">STORE</span> command. See the <a href="STORE.htm" target="" title="" alt="" class="MCXref_0">STORE</a> command for more information.</p>
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<p MadCap:conditions="BSEconditions.BSEWebHelp (Primary)-INCLUDE"><a href="../../HomeTopics/HomePage.htm">Go to Welcome page</a>
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<p style="text-align: right;"><span class="ContactInfoProjectName">BASIC Stamp Help</span> <![CDATA[ ]]><span class="ContactInfoVersion#">Version 2.5.4</span> <![CDATA[ ]]></p>
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<p style="text-align: right;">Copyright © <span class="ContactInfoCompanyName">Parallax Inc.</span></p>
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<p style="text-align: right;"><span class="SystemShortDate">8/8/2012</span>
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