126 lines
8.9 KiB
HTML
126 lines
8.9 KiB
HTML
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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>BUTTON</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">BUTTON</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" />
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</p>
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</div>
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<p style="text-align: right;"><a href="../ExampleTopics/ButtonEx.htm" target="" title="" alt="" class="MCXref_0">BUTTON 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">BUTTON</span> <![CDATA[ ]]><i>Pin</i>,<i> DownState</i>,<i> Delay</i>,<i> Rate</i>,<i> Workspace</i>,<i> TargetState</i>,<i> Address</i></p>
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<h2>Function</h2>
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<p class="PlainText">Monitor and process a pushbutton input, perform auto-repeat, and branch to address
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if button is in target state. Button circuits may be active-low or active-high.
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</p>
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<ul>
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<li value="1"><b><i>Pin</i></b> is a variable/constant/expression* (0 - 15) that specifies
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the I/O pin to use. This pin will be set to input mode.</li>
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<li value="2"><b><i>DownState</i></b> is a variable/constant/expression* (0 or 1) that
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specifies which logical state occurs when the button is pressed.</li>
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<li value="3"><b><i>Delay</i></b> is a variable/constant/expression* (0 - 255) that specifies
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how long the button must be pressed before auto-repeat starts. The delay is
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measured in cycles of the <span class="keyword_in_text">BUTTON</span> routine. <i>Delay</i> has two special
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settings: 0 and 255. If <i>Delay</i> is 0, <span class="keyword_in_text">BUTTON</span> performs no debounce
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or auto-repeat. If <i>Delay</i> is 255, Button performs debounce, but no
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auto-repeat. </li>
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<li value="4"><b><i>Rate</i></b> is a variable/constant/expression* (0 - 255) that specifies
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the number of cycles between auto-repeats. The rate is expressed in cycles
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of the <span class="keyword_in_text">BUTTON</span> routine. </li>
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<li value="5"><b><i>Workspace</i></b> is a byte variable used by <span class="keyword_in_text">BUTTON</span> for workspace.
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It must be cleared to 0 before being used by <span class="keyword_in_text">BUTTON</span> for the first time
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and should not be adjusted outside of the <span class="keyword_in_text">BUTTON</span> instruction. NOTE:
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All RAM is cleared to 0 by default upon power-up or reset of the BASIC
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Stamp. </li>
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<li value="6"><b><i>TargetState</i></b> is a variable/constant/expression* (0 or 1) that
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specifies which state the button should be in for a branch to occur (0=not
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pressed, 1=pressed).</li>
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<li value="7"><b><i>Address</i></b> is a label that specifies where to branch if the button
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is in the target state.</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. The range
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of the <i>Pin</i> argument on the BS1 is 0–7.</p>
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<h2>Explanation<br /></h2>
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<p class="PlainText">When you press a button or flip a switch, the contacts make or break a connection.
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A brief (1 to 20-ms) burst of noise occurs as the contacts scrape and bounce against
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each other. By scanning an input within a loop to ensure that the contact remains
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in a specified state for a minimum duration, spurious multiple inputs caused by
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contact noise can be eliminated. The <span class="keyword_in_text">BUTTON </span>instruction helps prevent this
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noise from being interpreted as more than one switch action; this is the function
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of the <i>Delay</i> parameter. (For a demonstration of switch bounce, see the demo
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program for the <a href="COUNT.htm" target="" title="" alt="" class="MCXref_0">COUNT</a> instruction.) <i>Delay</i>, combined
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with the <i>Rate</i> parameter, allows the programmer to control the rate at which
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multiple inputs are accepted by the BASIC Stamp.</p>
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<p class="PlainText"><span class="keyword_in_text">BUTTON</span> also lets PBASIC react to a button press the way your computer
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keyboard does to a key press. When you press a key, a character immediately appears
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on the screen. If you hold the key down, there's a delay, then a rapid-fire stream
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of characters appears on the screen. <span class="keyword_in_text">BUTTON</span>'s auto-repeat function can be
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set up to work much the same way. </p>
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<p class="PlainText"><span class="keyword_in_text">BUTTON</span> is designed for use inside a program loop. Each time through the
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loop, <span class="keyword_in_text">BUTTON</span> checks the state of the specified pin. When it first matches
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<i>DownState</i>, <span class="keyword_in_text">BUTTON</span> begins the <i>Delay</i> countdown for auto-repeat.
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Then, in accordance with <i>TargetState</i>, it either branches to address
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(TargetState = 1) or doesn't (TargetState = 0).</p>
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<p class="PlainText">If the switch stays in <i>DownState</i>, <span class="keyword_in_text">BUTTON</span> counts the number of
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program loops that execute. When this count equals <i>Delay</i>, <span class="keyword_in_text">BUTTON</span>once again triggers the action specified by <i>TargetState</i> and <i>Address</i>. Hereafter,
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if the switch remains in <i>DownState</i>, <span class="keyword_in_text">BUTTON</span> waits <i>Rate</i> number
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of cycles between actions. The <i>Workspace</i> variable is used by <span class="keyword_in_text">BUTTON</span>
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to keep track of how many cycles have occurred since the pin switched to
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<i>TargetState</i> or since the last auto-repeat.</p>
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<p class="PlainText"><span class="keyword_in_text">BUTTON</span> does not stop program execution. In order for its delay and auto
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repeat functions to work properly, <span class="keyword_in_text">BUTTON</span> must be executed from within a
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program loop.</p>
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<center>
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<img src="../../graphics/button_sch.gif" border="0" />
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</center>
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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>
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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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