205 lines
13 KiB
HTML
205 lines
13 KiB
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<?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>EEPROM</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">EEPROM</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" /><span class="code_in_text"> {PBASIC 1.0}</span>
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</p>
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</div>
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<p style="text-align: right;"><a href="../ExampleTopics/EepromEx.htm" target="" title="" alt="" class="MCXref_0" xrefformat="{paratext}">EEPROM Example</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: <span class="keyword_in_text">EEPROM</span> {<i>Location</i>,} (<i> DataItem
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</i>{,<i> DataItem</i>,...})</p>
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<h2>Function</h2>
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<p class="PlainText">Write data to the EEPROM during program download.</p>
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<ul>
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<li value="1"><b><i>Location</i></b> is an optional variable/constant (0 - 255) that
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specifies the starting location in the EEPROM at which data should be stored.
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If no location is given, data is written starting at the next available
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location.</li>
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<li value="2"><b><i>DataItem</i></b> is a constant (0 - 255) to be stored in EEPROM.</li>
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</ul>
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<h2>Quick Facts</h2>
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<table cellpadding="4" cellspacing="0" border="1" style="caption-side: top;width: 100%;">
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<col />
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<col />
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<tr bgcolor="#CFCFCF">
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<td width="15%" align="center"> </td>
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<td width="85%" align="center">BS1</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>Writes values to EEPROM during download. Can be used to decrease program size.</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>
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<p colspan="2" align="center"><a href="READ.htm" target="" title="" alt="" class="MCXref_0" xrefformat="{paratext}">READ</a>, <a href="WRITE.htm" target="" title="" alt="" class="MCXref_0" xrefformat="{paratext}">WRITE</a></p>
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</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">When you download a program into the BASIC Stamp 1, it is stored in the EEPROM
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starting at the highest address (255) and working towards the lowest address. Most
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programs don't use the entire EEPROM, so the lower portion is available for other
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uses. The <span class="keyword_in_text">EEPROM</span> directive allows you to define a set of data to store in
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the available EEPROM locations. It is called a "directive" rather than a "command"
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because it performs an activity at compile-time rather than at run-time (i.e., the
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<span class="keyword_in_text">EEPROM</span> directive is not downloaded to the BASIC Stamp 1, but the data it
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contains is downloaded).</p>
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<p>The simplest form of the <span class="keyword_in_text">EEPROM</span> directive is something like the following:</p><pre class="BScode" xml:space="preserve">
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EEPROM (100, 200, 52, 45)
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</pre>
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<p class="PlainText">This example, when downloaded, will cause the values 100, 200, 52 and 45 to be
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written to EEPROM locations 0, 1, 2 and 3, respectively. You can then use the
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<span class="keyword_in_text">READ</span> and <span class="keyword_in_text">WRITE</span> commands in your code to access these locations and
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the data you've stored there</p>
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<p class="PlainText">The <span class="keyword_in_text">EEPROM</span> directive uses a counter, called a pointer, to keep track of
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available EEPROM addresses. The value of the pointer is initially 0. When a program
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is downloaded, the <span class="keyword_in_text">EEPROM</span> directive stores the first byte value at the current
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pointer address, then increments (adds 1 to) the pointer. If the program contains
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more than one <span class="keyword_in_text">EEPROM</span> directive, subsequent <span class="keyword_in_text">EEPROM</span> directives start
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with the pointer value left by the previous <span class="keyword_in_text">EEPROM</span> directive. For example,
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if the program contains:</p><pre class="BScode" xml:space="preserve">
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EEPROM (72, 69, 76, 76, 79)
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EEPROM (104, 101, 108, 108, 111)
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</pre>
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<p class="PlainText">The first <span class="keyword_in_text">EEPROM</span> directive will start at location 0 and increment the
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pointer for each data value it stores (1, 2, 3, 4 and 5). The second <span class="keyword_in_text">EEPROM</span>directive will start with the pointer value of 5 and work upward from there. As
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a result, the first 10 bytes of EEPROM will look like the following:</p>
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<table width="100%" cellpadding="4" cellspacing="0" border="1">
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<tr>
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<td width="20%" align="center" bgcolor="#CFCFCF" rowspan="2"> </td>
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<td align="center" bgcolor="#CFCFCF" colspan="10">EEPROM Location (address)</td>
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</tr>
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<tr>
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<td width="8%" align="center" bgcolor="#CFCFCF">0</td>
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<td width="8%" align="center" bgcolor="#CFCFCF">1</td>
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<td width="8%" align="center" bgcolor="#CFCFCF">2</td>
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<td width="8%" align="center" bgcolor="#CFCFCF">3</td>
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<td width="8%" align="center" bgcolor="#CFCFCF">4</td>
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<td width="8%" align="center" bgcolor="#CFCFCF">5</td>
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<td width="8%" align="center" bgcolor="#CFCFCF">6</td>
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<td width="8%" align="center" bgcolor="#CFCFCF">7</td>
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<td width="8%" align="center" bgcolor="#CFCFCF">8</td>
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<td width="8%" align="center" bgcolor="#CFCFCF">9</td>
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</tr>
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<tr>
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<td width="20%" align="center" bgcolor="#CFCFCF">Contents</td>
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<td width="8%" align="center">72</td>
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<td width="8%" align="center">69</td>
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<td width="8%" align="center">76</td>
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<td width="8%" align="center">76</td>
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<td width="8%" align="center">79</td>
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<td width="8%" align="center">104</td>
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<td width="8%" align="center">101</td>
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<td width="8%" align="center">108</td>
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<td width="8%" align="center">108</td>
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<td width="8%" align="center">111</td>
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</tr>
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</table>
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<p class="PlainText">What if you don't want to store values starting at location 0? Fortunately,
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the <span class="keyword_in_text">EEPROM</span> directive has an option to specify the next location to use.
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You can specify the next location number (to set the pointer to) by using the
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optional <i>Location</i> argument before the list of <i>DataItems</i>. The following
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code writes the same data in the table above to locations 50 through 59:</p><pre class="BScode" xml:space="preserve">
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EEPROM 50, (72, 69, 76, 76, 79, 104, 101, 108, 108, 111)
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</pre>
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<p class="PlainText">In this example, the <i>Location</i> argument is given and tells the <span class="keyword_in_text">EEPROM</span>directive to store the following <i>DataItem</i>(s) starting at location 50. The
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<i>DataItems</i> in the list are stored in their respective locations (50, 51,
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52... 59).</p>
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<p class="PlainText">It is important to realize that the entire BASIC Stamp 1 EEPROM is overwritten
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during programming. Any EEPROM location not containing a PBASIC program or
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<i>DataItems</i> from an <span class="keyword_in_text">EEPROM</span> directive is written with a 0. </p>
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<p class="PlainText">A common use for EEPROM is to store strings; sequences of bytes representing
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text. PBASIC converts quoted text like "A" into the corresponding ASCII character
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code (65 in this case). To make data entry easier, you can place quotes around a
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whole chunk of text used in a <span class="keyword_in_text">EEPROM</span> directive, and PBASIC will understand
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it to mean a series of bytes (see the last line of code below). The following three
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<span class="keyword_in_text">EEPROM</span> directives are equivalent: </p><pre class="BScode" xml:space="preserve">
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EEPROM (72, 69, 76, 76, 79)
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EEPROM ("H", "E", "L", "L", "O")
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EEPROM ("HELLO")
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</pre>
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<p class="PlainText">All three lines of code, above, will result in the numbers 72, 69, 76, 76, and
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79 being stored into EEPROM upon downloading. These numbers are simply the ASCII
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character codes for "H", "E", "L", "L", and "O", respectively. See the
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Example program above for a demonstration of storing and
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reading multiple text strings.</p>
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<p class="PlainText">The EEPROM is organized as a sequential set of byte-sized memory locations.
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The <span class="keyword_in_text">EEPROM</span> directive only stores bytes into EEPROM. If you try to store
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a word-size value, for example: <span class="keyword_in_text">EEPROM</span> (1125), only the lower byte of the
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value will be stored (in this case, 101). This does not mean that you can't store
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word-sized values, however. A word consists of two bytes, called a low-byte and
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a high-byte. If you wanted to store the value 1125 using the <span class="keyword_in_text">EEPROM</span> directive
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you'll have to calculate the low-byte and the high-byte and insert them in the
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list in the proper order, as in:</p><pre class="BScode" xml:space="preserve">
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EEPROM (101, 4)
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</pre>
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<p class="PlainText">The directive above will store the two bytes into two sequential EEPROM
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locations (the low-byte first, followed by the high-byte). We calculated this in
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the following manner: 1) high-byte is INT(value / 256) and 2) low-byte is value -
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(high-byte * 256).</p>
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<p class="PlainText">To retrieve a word-size value, you'll need to use two <span class="keyword_in_text">READ</span> commands and
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a word-size variable. For example,</p><pre class="BScode" xml:space="preserve">
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SYMBOL result = W1 ' word-sized variable
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SYMBOL resLo = B2 ' B2 is low-byte of W1
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SYMBOL resHi = B3 ' B3 is high-byte of W1
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EEPROM (101, 4)
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Main:
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READ 0, resLo
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READ 1, resHi
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DEBUG #result
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END
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</pre>
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<p class="PlainText">This code would write the low-byte and high-byte of the number 1125 into
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locations 0 and 1 during download. When the program runs, the two <span class="keyword_in_text">READ</span>commands will read the low-byte and high-byte out of EEPROM (reconstructing it in
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a word-size variable) and then display the value on the screen. See the <a href="READ.htm" target="" title="" alt="" class="MCXref_0" xrefformat="{paratext}">READ</a>
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and <a href="WRITE.htm" target="" title="" alt="" class="MCXref_0" xrefformat="{paratext}">WRITE</a> commands for more
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information.</p>
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<div class="Col2">
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<div class="MasterFoot">
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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>
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</div>
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<div class="Col2">
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<div class="MasterFoot">
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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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</p>
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</div>
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