205 lines
12 KiB
HTML
205 lines
12 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>SHIFTIN</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">SHIFTIN</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_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/ShiftinEx.htm" target="" title="" alt="" class="MCXref_0" xrefformat="{paratext}">SHIFTIN 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">SHIFTIN</span> <![CDATA[ ]]><i>Dpin</i>,<i> Cpin</i>,<i> Mode</i>,<i><![CDATA[ ]]></i>[<i>Variable </i>{\<i>Bits</i>} {,<i> Variable </i>{\<i>Bits</i>}...}]</p>
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<h2>Function</h2>
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<p class="PlainText">Shift data in from a synchronous serial device.
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</p>
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<ul>
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<li value="1"><b><i>Dpin</i></b> is a variable/constant/expression (0 - 15) that specifies
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the I/O pin that will be connected to the synchronous serial device's data
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output. This pin will be set to input mode.</li>
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<li value="2"><b><i>Cpin</i></b> is a variable/constant/expression (0 - 15) that specifies
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the I/O pin that will be connected to the synchronous serial device's clock
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input. This pin will be set to output mode.</li>
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<li value="3"><b><i>Mode</i></b> is a variable/constant/expression (0 - 3), or one of four
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predefined symbols, that tells <span class="keyword_in_text">SHIFTIN</span> the order in which data bits are
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to be arranged and the relationship of clock pulses to valid data. See the
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table below for value and symbol definitions.</li>
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<li value="4"><b><i>Variable</i></b> is a variable in which incoming data bits will be
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stored.</li>
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<li value="5"><b><i>Bits</i></b> is an optional variable/constant/expression (1 - 16)
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specifying how many bits are to be input by <span class="keyword_in_text">SHIFTIN</span>. If no <i>Bits</i>
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entry is given, <span class="keyword_in_text">SHIFTIN</span> defaults to 8 bits.</li>
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</ul>
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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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<tr bgcolor="#CFCFCF">
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<td width="250" align="center"> </td>
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<td width="25%" align="center">BS2, BS2e, and BS2pe</td>
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<td width="25%" align="center">BS2sx and BS2p</td>
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<td width="25%" align="center">BS2px</td>
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</tr>
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<tr>
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<td align="center" bgcolor="#CFCFCF">Timing of T<sub>0</sub> and T<sub>1</sub></td>
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<td align="center">14 µs / 46 µs</td>
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<td align="center">5.6 µs / 18 µs</td>
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<td align="center">3.6 µs / 11.8 µs</td>
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</tr>
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<tr>
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<td align="center" bgcolor="#CFCFCF">Transmission Rate</td>
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<td align="center">~ 16 kBits/Sec</td>
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<td align="center">~ 42 kBits/Sec</td>
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<td align="center">~ 65 kBits/Sec</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="3">
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<p colspan="3" align="center"><a href="SHIFTOUT.htm" target="" title="" alt="" class="MCXref_0" xrefformat="{paratext}">SHIFTOUT</a>
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</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"><span class="keyword_in_text">SHIFTIN</span> and <span class="keyword_in_text">SHIFTOUT</span> provide an easy method of acquiring data from
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synchronous serial devices. Synchronous serial differs from asynchronous serial
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(like <span class="keyword_in_text">SERIN</span> and <span class="keyword_in_text">SEROUT</span>) in that the timing of data bits (on a data
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line) is specified in relationship to clock pulses (on a clock line). Data bits
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may be valid after the rising or falling edge of the clock line. This kind of
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serial protocol is commonly used by controller peripherals like ADCs, DACs, clocks,
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memory devices, etc. </p>
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<p class="PlainText">At their heart, synchronous-serial devices are essentially shift-registers;
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trains of flip-flops that pass data bits along in a bucket brigade fashion to a
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single data output pin. Another bit is output each time the appropriate edge
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(rising or falling, depending on the device) appears on the clock line. </p>
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<p class="PlainText">The <span class="keyword_in_text">SHIFTIN</span> instruction first causes the clock pin to output low and
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the data pin to switch to input mode. Then, <span class="keyword_in_text">SHIFTIN</span> either reads the data
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pin and generates a clock pulse (PRE mode) or generates a clock pulse then reads
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the data pin (POST mode). <span class="keyword_in_text">SHIFTIN</span> continues to generate clock pulses and
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read the data pin for as many data bits as are required.</p>
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<p class="PlainText">Making <span class="keyword_in_text">SHIFTIN</span> work with a particular device is a matter of matching
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the mode and number of bits to that device's protocol. Most manufacturers use a
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timing diagram to illustrate the relationship of clock and data. Items to look
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for include: 1) which bit of the data arrives first; most significant bit (MSB)
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or least significant bit (LSB) and 2) is the first data bit ready before the
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first clock pulse (PRE) or after the first clock pulse (POST). The table below
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shows the values and symbols available for the <i>Mode</i> argument.</p>
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<table width="100%" cellpadding="4" cellspacing="0" border="1">
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<tr bgcolor="#CFCFCF">
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<td width="75" align="center">Symbol</td>
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<td width="65" align="center">Value</td>
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<td width="80%" align="center">Meaning</td>
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</tr>
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<tr>
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<td align="center">MSBPRE</td>
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<td align="center">0</td>
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<td align="left">Data is MSB-first; sample bits before clock pulse</td>
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</tr>
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<tr>
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<td align="center">LSBPRE</td>
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<td align="center">1</td>
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<td align="left">Data is lsb-first; sample bits before clock pulse</td>
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</tr>
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<tr>
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<td align="center">MSBPOST</td>
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<td align="center">2</td>
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<td align="left">Data is MSB-first; sample bits after clock pulse</td>
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</tr>
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<tr>
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<td align="center">LSBPOST</td>
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<td align="center">3</td>
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<td align="left">Data is LSB-first; sample bits after clock pulse</td>
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</tr>
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</table>
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<h3>SHIFTIN Timing</h3>
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<center>
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<img src="../../graphics/shiftin_timing.gif" border="0">
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</img>
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</center>
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<p class="PlainText">Here is a simple example:</p><pre class="BScode" xml:space="preserve">
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result VAR Byte
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Main:
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SHIFTIN 0, 1, MSBPRE, [result]
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END
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</pre>
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<p class="PlainText">Here, the <span class="keyword_in_text">SHIFTIN</span> command will read I/O pin 0 (the Dpin) and will
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generate a clock signal on I/O 1 (the <i>Cpin</i>). The data that arrives on the
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Dpin depends on the device connected to it. Let's say, for example, that a shift
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register is connected and has a value of $AF (10101111) waiting to be sent.
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Additionally, let's assume that the shift register sends out the most significant
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bit first, and the first bit is on the <i>Dpin</i> before the first clock pulse
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(MSBPRE). The <span class="keyword_in_text">SHIFTIN</span> command above will generate eight clock pulses and
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sample the data pin (<i>Dpin</i>) eight times. Afterward, the result variable
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will contain the value $AF.</p>
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<p class="PlainText">By default, <span class="keyword_in_text">SHIFTIN</span> acquires eight bits, but you can set it to shift
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any number of bits from 1 to 16 with the <i>Bits</i> argument. For example:</p><pre class="BScode" xml:space="preserve">
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result VAR Byte
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Main:
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SHIFTIN 0, 1, MSBPRE, [result\4]
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END
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</pre>
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<p class="PlainText">Will only input the first 4 bits. In the example discussed above, the result
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variable will be left with %1010. </p>
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<p class="PlainText">Some devices return more than 16 bits. For example, most 8-bit shift registers
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can be daisy-chained together to form any multiple of 8 bits; 16, 24, 32, 40...
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To solve this, you can use a single <span class="keyword_in_text">SHIFTIN</span> instruction with multiple
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variables. Each variable can be assigned a particular number of bits with the
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<i>Bits</i> argument. As in: </p><pre class="BScode" xml:space="preserve">
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dataLo VAR Word
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dataHi VAR Byte
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Main:
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SHIFTIN 0, 1, MSBPRE, [dataHi\4, dataLo\16]
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STOP
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</pre>
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<p class="PlainText">The code above will first shift in four bits into dataHi and then 16 bits
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into dataLo. The two variables together make up a 20 bit value.</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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