3839.htm

Labview 访问2线制数据i2C

<b>手动控制</b><p>

<img src=http://www.maxim-ic.com.cn/images/appnotes/3839/3839Fig04.jpg alt="Figure 4. The MANUAL control tab lets the user define the number of bytes and intended read or write operation."><br> <i>图4. MANUAL控制标签允许用户定义操作的字节数以及期望的读或写操作。</i><p>

用户利用<b>MANUAL</b>控制选项(<b>图4</b>)，来决定字节数和所需的操作。下面给出了标准单字节写操作和双字节读操作的例子。<p>

<b>单字节写操作</b>
<table border="0" cellspacing="1" cellpadding="2">
 <tr class="tablebody">
   <td><pre>START</pre></td>
   <td><pre>SEND WRITE (DEVICE<br>ADDRESS FOR WRITE)</pre></td>
   <td><pre>SEND BYTE (MEMORY<br>ADDRESS)</pre></td>
   <td><pre>SEND BYTE (DATA TO<br>BE WRITTEN)</pre></td>
   <td><pre>STOP</pre></td>
 </tr>
</table><br>
				

<b>双字节读操作</b>
<table border="0" cellspacing="1" cellpadding="2">
 <tr class="tablebody">
   <td><pre>START</pre></td>
   <td><pre>SEND WRITE<br>(DEVICE<br>ADDRESS<br>FOR WRITE)</pre></td>
   <td><pre>SEND BYTE<br>(MEMORY<br>ADDRESS)</pre></td>
   <td><pre>SEND<br>START<br>(REPEATED<br>START)</pre></td>
   <td><pre>SEND READ<br>(DEVICE<br>ADDRESS<br>FOR READ)</pre></td>
   <td><pre>READ WITH<br>ACK (READ<br>1ST BYTE)</pre></td>
   <td><pre>READ WITH<br>NACK (READ<br>2ND BYTE)</pre></td>
   <td><pre>STOP</td>
 </tr>
</table><br>
							

<b>重要提示：</b>当读数据时，最后一个读取的字节应该采用“Read with NACK”。这允许用户根据需要读取多个字节。需要“Read with NACK”以告知设备不要再发送更多数据。<p>

用户可以复位I<sup>2</sup>C总线。如果用户在手动控制的通信过程中不知怎样操作，并且总线处于未知状态，那么这个功能非常有用。<b>SCL</b>和<b>SDA</b> High/Low (高/低)按钮允许用户将这些引脚强制为期望的状态。<p>

<h2>总结</h2>
本应用笔记结合提供的LabView VI，阐述了与DS3900通信时LabView起到的巨大作用。一旦理解了这些基本概念，用户就可以修改VI或者复制特定模块，以满足特定的应用需求。<p>
	
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	APP 3839: Nov 09, 2006
	
	




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	<td valign=top width='60%'>串口通信模块，配合评估板使用</td>
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			<a href="/getds.cfm?qv_pk=4968">完整的数据资料</a><br>(PDF, 884kB)
		
	
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