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8.9 KiB
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155 lines
8.9 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="PBASIC Language Reference" 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>PIN</title>
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<link href="../../SkinSupport/MadCap.css" rel="stylesheet" />
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</head>
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<body>
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<div class="MCBreadcrumbsBox_0"><span class="MCBreadcrumbsPrefix">You are here: </span><a class="MCBreadcrumbsLink" href="AlphaRef.htm">PBASIC Language Reference</a><span class="MCBreadcrumbsDivider"> > </span><span class="MCBreadcrumbs">PIN Directive</span>
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</div>
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<h1 class="code">PIN</h1>
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<p>
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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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<p class="PlainText"> </p>
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<p class="PlainText">This section discusses the <span class="keyword_in_text">PIN </span>directive available with PBASIC 2.5</p>
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<p class="PlainText">(For BASIC Stamp I/O pin definitions and ratings, see <a href="../../HardwareTopics/PinDesc.htm" target="" title="" alt="" class="MCXref_0">Pin Descriptions</a>)</p>
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<p class="PlainText">(For BS2px I/O pin commands, see <a href="../Commands/COMPARE.htm" target="" title="" alt="" class="MCXref_0">COMPARE</a> and <a href="../Commands/CONFIGPIN.htm" target="" title="" alt="" class="MCXref_0">CONFIGPIN</a>.)</p>
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<p class="PlainText">With the introduction of PBASIC 2.5 syntax comes the <span class="keyword_in_text">PIN</span> directive. The
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purpose of the <span class="keyword_in_text">PIN </span>directive is to give an alias to an I/O pin and let the
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compiler determine whether a given line of code requires a numeric value for the
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pin, the output bit for that pin, or the input bit for that pin. Using the <span class="keyword_in_text">PIN</span> directive simplifies I/O pin aliasing in sophisticated programs.</p>
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<h2>PIN Syntax</h2>
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<p class="PlainText">Syntax: <i>PIN_Symbol</i> <![CDATA[ ]]><span class="keyword_in_text">PIN</span><i>Pin_Number</i></p>
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<ul>
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<li value="1"><b><i>PIN_Symbol</i></b> is a unique symbol name that will be
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used as an alias for the I/O pin number <i>Pin_Number</i>.</li>
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<li value="2"><b><i>Pin_Number</i></b> is an I/O pin number (0 to 15)</li>
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</ul>
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<h2>Summary of PIN Behaviors in Context</h2>
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<p class="PlainText"><i>PIN_Symbol</i> behaves like a constant:</p>
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<ol>
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<li value="1">...when used in a command’s <i>Pin</i> argument. Example:</li>
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</ol><pre class="snippet">OUTPUT PIN_Symbol</pre>
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<ol MadCap:continue="true">
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<li value="2">...when used in the index of an array. Example:</li>
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</ol><pre class="snippet">myArray(PIN_Symbol) = 25</pre>
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<p class="PlainText"><i>PIN_Symbol</i> behaves like an input variable (INx):</p>
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<ol>
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<li value="1">...when used in a command’s non-Pin argument that expects to read a variable/constant/expression. Example:</li>
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</ol><pre class="snippet">DEBUG BIN PIN_Symbol</pre>
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<ol MadCap:continue="true">
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<li value="2">...when used in a command’s <i>Condition</i> argument. Example:</li>
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</ol><pre class="snippet">IF PIN_Symbol = 1 THEN…</pre>
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<ol MadCap:continue="true">
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<li value="3">...when used to the right of the equal sign (=) in an assignment statement. Example:</li>
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</ol><pre class="snippet">myVariable = PIN_Symbol + 1</pre>
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<p class="PlainText"><i>PIN_Symbol</i> behaves like an output variable (OUTx):</p>
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<ol>
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<li value="1">...when used in a command’s non-<i>Pin</i> argument that expects to write a result to a variable. Example:</li>
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</ol><pre class="snippet">LOOKUP index, [0, 1, 1, 0, 1], PIN_Symbol</pre>
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<ol MadCap:continue="true">
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<li value="2">...when used to the left of the equal sign (=) in an assignment statement. Example:</li>
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</ol><pre class="snippet">PIN_Symbol = 1</pre>
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<h2>PIN Examples</h2>
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<p class="PlainText">Using the <span class="keyword_in_text">PIN</span> declaration is similar to <span class="keyword_in_text">CON</span>:</p><pre class="BScode" xml:space="preserve">
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' {$PBASIC 2.5}
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RedLED PIN 0 ' red LED is connected to pin 0
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IsOn CON 1 ' LED is active high
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IsOff CON 0
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Setup:
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OUTPUT RedLED ' same as OUTPUT 0
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Main:
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DO
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RedLED = IsOn ' same as Out0 = 1
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PAUSE 1000
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RedLED = IsOff ' same as Out0 = 0
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PAUSE 1000
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LOOP
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</pre>
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<p class="PlainText">Most programs will work like the example above where a given I/O pin will
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either be an input or an output. There are times, however, when a change in
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function is required mid program. Prior to PBASIC 2.5, programmers wishing to
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use named constants were forced to create redundant definitions or complicated
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modifiers. For example:</p><pre class="BScode" xml:space="preserve">
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' {$PBASIC 2.0}
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SDA CON 8 ' I2C data I/O
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SCL CON 9 ' I2C clock output
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...
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I2C_Start:
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INPUT SDA
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INPUT SCL
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LOW SDA
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Clock_Hold: ' monitor device clock hold
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IF (INS.LOWBIT(SCL) = 0) THEN Clock_Hold ' <-- tricky modifiers
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RETURN
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</pre>
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<p class="PlainText">With PBASIC 2.5 the tricky modifiers can be eliminated:</p><pre class="BScode" xml:space="preserve">
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' {$PBASIC 2.5}
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SDA PIN 8 ' I2C data I/O
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SCL PIN 9 ' I2C clock output
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...
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I2C_Start:
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INPUT SDA
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INPUT SCL
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LOW SDA
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Clock_Hold: ' monitor device clock hold
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DO : LOOP WHILE (SCL = 0) ' easier, same as "IN9 = 0"
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RETURN
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</pre>
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<p class="PlainText">The compiler is "smart" and knows how to replace a <span class="keyword_in_text">PIN</span> directive with a
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constant value, an INS register bit or and OUTS register bit. Note that as in
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the example above, the programmer is still responsible for setting the DIRS bit
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of the I/O pin as required by the program.</p>
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<p class="PlainText"> </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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<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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