通讯总线知识第二课：RS-232、RS-422与RS-485...

<p style="LINE-HEIGHT: 150%; MARGIN-TOP: 0pt; MARGIN-BOTTOM: 0pt" class="p0"><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; FONT-WEIGHT: bold; mso-spacerun: 'yes'">一、</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; FONT-WEIGHT: bold; mso-spacerun: 'yes'">RS-232</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; FONT-WEIGHT: bold; mso-spacerun: 'yes'">、</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; FONT-WEIGHT: bold; mso-spacerun: 'yes'">RS-422</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; FONT-WEIGHT: bold; mso-spacerun: 'yes'">与</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; FONT-WEIGHT: bold; mso-spacerun: 'yes'">RS-485</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; FONT-WEIGHT: bold; mso-spacerun: 'yes'">由来</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; FONT-WEIGHT: bold; mso-spacerun: 'yes'"><?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" /><o:p></o:p></span></p>
<p style="LINE-HEIGHT: 150%; MARGIN-TOP: 0pt; TEXT-INDENT: 12pt; MARGIN-BOTTOM: 0pt" class="p0"><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">RS-232</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">、</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">RS-422</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">与</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">RS-485</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">都是串行数据接口标准，最初都是由电子工业协会(</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">EIA</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">)制订并发布的，</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">RS-232</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">在</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">1962</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">年发布，命名为</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">EIA-232-E</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">，作为工业标准，以保证不同厂家产品之间的兼容。</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">RS-422</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">由</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">RS-232</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">发展而来，它是为弥补</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">RS-232</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">之不足而提出的。为改进</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">RS-232</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">通信距离短、速率低的缺点，</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">RS-422</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">定义了一种平衡通信接口，将传输速率提高到</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">10Mb/s</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">，传输距离延长到</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">4000</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">英尺(速率低于</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">100kb/s</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">时)，并允许在一条平衡总线上连接最多</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">10</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">个接收器。</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">RS-422</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">是一种单机发送、多机接收的单向、平衡传输规范，被命名为</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">TIA/EIA-422-A</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">标准。为扩展应用范围，</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">EIA</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">又于</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">1983</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">年在</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">RS-422</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">基础上制定了</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">RS-485</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">标准，增加了多点、双向通信能力，即允许多个发送器连接到同一条总线上，同时增加了发送器的驱动能力和冲突保护特性，扩展了总线共模范围，后命名为</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">TIA/EIA-485-A</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">标准。由于</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">EIA</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">提出的建议标准都是以</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">"RS"</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">作为前缀，所以在通讯工业领域，仍然习惯将上述标准以</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">RS</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">作前缀称谓。</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'"><o:p></o:p></span></p>
<p style="LINE-HEIGHT: 150%; MARGIN-TOP: 0pt; TEXT-INDENT: 107.4pt; MARGIN-BOTTOM: 0pt" class="p0"><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'"><br/></span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">　　</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">RS-232</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">、</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">RS-422</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">与</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">RS-485</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">标准只对接口的电气特性做出规定，而不涉及接插件、电缆或协议，在此基础上用户可以建立自己的高层通信协议。因此在视频界的应用，许多厂家都建立了一套高层通信协议，或公开或厂家独家使用。如录像机厂家中的</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">Sony</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">与松下对录像机的</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">RS-422</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">控制协议是有差异的，视频服务器上的控制协议则更多了，如</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">Louth</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">、</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">Odetis</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">协议是公开的，而</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">ProLINK</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">则是基于</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">Profile</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">上的。</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'"><o:p></o:p></span></p>
<p style="LINE-HEIGHT: 150%; MARGIN-TOP: 0pt; TEXT-INDENT: 107.4pt; MARGIN-BOTTOM: 0pt" class="p0"><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; FONT-WEIGHT: bold; mso-spacerun: 'yes'"><o:p></o:p></span></p>
<p style="LINE-HEIGHT: 150%; MARGIN-TOP: 0pt; MARGIN-BOTTOM: 0pt" class="p0"><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; FONT-WEIGHT: bold; mso-spacerun: 'yes'">二、</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; FONT-WEIGHT: bold; mso-spacerun: 'yes'">RS-422</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; FONT-WEIGHT: bold; mso-spacerun: 'yes'">与</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; FONT-WEIGHT: bold; mso-spacerun: 'yes'">RS-485</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; FONT-WEIGHT: bold; mso-spacerun: 'yes'">串行接口标准</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; FONT-WEIGHT: bold; mso-spacerun: 'yes'">&nbsp;</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'"><br/></span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'"><br/></span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">　　</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">1</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">．平衡传输</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">&nbsp;</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'"><br/></span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">　　</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">RS-422</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">、</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">RS-485</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">与</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">RS-232</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">不一样，数据信号采用差分传输方式，也称作平衡传输，它使用一对双绞线，将其中一线定义为</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">A</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">，另一线定义为</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">B</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">。</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'"><br/></span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'"><br/></span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">　　通常情况下，发送驱动器</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">A</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">、</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">B</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">之间的正电平在</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">+2</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">～</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">+6V</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">，是一个逻辑状态，负电平在</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">-2</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">～</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">6V</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">，是另一个逻辑状态。另有一个信号地</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">C</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">，在</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">RS-485</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">中还有一</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">"</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">使能</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">"</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">端，而在</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">RS-422</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">中这是可用可不用的。</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">"</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">使能</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">"</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">端是用于控制发送驱动器与传输线的切断与连接。当</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">"</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">使能</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">"</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">端起作用时，发送驱动器处于高阻状态，称作</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">"</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">第三态</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">"</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">，即它是有别于逻辑</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">"1"</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">与</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">"0"</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">的第三态。</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'"><br/></span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'"><br/></span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">　　接收器也作与发送端相对的规定，收、发端通过平衡双绞线将</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">AA</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">与</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">BB</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">对应相连，当在收端</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">AB</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">之间有大于</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">+200mV</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">的电平时，输出正逻辑电平，小于</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">-200mV</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">时，输出负逻辑电平。接收器接收平衡线上的电平范围通常在</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">200mV</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">至</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">6V</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">之间。</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'"><br/></span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'"><br/></span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">　　</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">2</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">．</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">RS-422</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">电气规定</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">&nbsp;</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'"><br/></span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">　　</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">RS-422</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">标准全称是</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">"</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">平衡电压数字接口电路的电气特性</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">"</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">，它定义了接口电路的特性。实际上还有一根信号地线，共</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">5</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">根线。图</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">4</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">是其</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">DB9</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">连接器引脚定义。由于接收器采用高输入阻抗和发送驱动器比</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">RS232</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">更强的驱动能力，故允许在相同传输线上连接多个接收节点，最多可接</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">10</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">个节点。即一个主设备(</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">Master</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">)，其余为从设备(</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">Salve</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">)，从设备之间不能通信，所以</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">RS-422</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">支持点对多的双向通信。接收器输入阻抗为</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">4k</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">，故发端最大负载能力是</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">10</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">×</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">4k+100</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">Ω(终接电阻)。</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">RS-422</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">四线接口由于采用单独的发送和接收通道，因此不必控制数据方向，各装置之间任何必须的信号交换均可以按软件方式(</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">XON/XOFF</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">握手)或硬件方式(一对单独的双绞线)实现。</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'"><br/></span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'"><br/></span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">　　</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">RS-422</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">的最大传输距离为</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">4000</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">英尺(约</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">1219</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">米)，最大传输速率为</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">10Mb/s</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">。其平衡双绞线的长度与传输速率成反比，在</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">100kb/s</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">速率以下，才可能达到最大传输距离。只有在很短的距离下才能获得最高速率传输。一般</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">100</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">米长的双绞线上所能获得的最大传输速率仅为</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">1Mb/s</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">。</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">&nbsp;</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'"><br/></span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">RS-422</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">需要一终接电阻，要求其阻值约等于传输电缆的特性阻抗。在矩距离传输时可不需终接电阻，即一般在</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">300</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">米以下不需终接电阻。终接电阻接在传输电缆的最远端。</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'"><br/></span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'"><o:p></o:p></span></p>
<p style="LINE-HEIGHT: 150%; MARGIN-TOP: 0pt; MARGIN-BOTTOM: 0pt" class="p0"><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'"><br/></span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">　　</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">3</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">．</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">RS-485</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">电气规定</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">&nbsp;</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'"><br/></span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">　　由于</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">RS-485</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">是从</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">RS-422</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">基础上发展而来的，所以</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">RS-485</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">许多电气规定与</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">RS-422</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">相仿。如都采用平衡传输方式、都需要在传输线上接终接电阻等。</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">RS-485</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">可以采用二线与四线方式，二线制可实现真正的多点双向通信。</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'"><br/></span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'"><br/></span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">　　而采用四线连接时，与</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">RS-422</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">一样只能实现点对多的通信，即只能有一个主(</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">Master</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">)设备，其余为从设备，但它比</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">RS-422</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">有改进，</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">&nbsp;</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">无论四线还是二线连接方式总线上可多接到</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">32</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">个设备。</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'"><br/></span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'"><br/></span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">　　</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">RS-485</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">与</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">RS-422</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">的不同还在于其共模输出电压是不同的，</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">RS-485</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">是</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">-7V</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">至</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">+12V</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">之间，而</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">RS-422</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">在</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">-7V</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">至</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">+7V</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">之间，</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">RS-485</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">接收器最小输入阻抗为</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">12k</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">欧，</span><span style="FONT-FAMILY: 'MingLiU_HKSCS'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">?</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">而</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">RS-422</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">是</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">4k</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">欧。</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'"><br/></span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'"><br/></span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">　　</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">RS-485</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">与</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">RS-422</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">一样，其最大传输距离约为</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">1219</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">米，最大传输速率为</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">10Mb/s</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">。平衡双绞线的长度与传输速率成反比，在</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">100kb/s</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">速率以下，才可能使用规定最长的电缆长度。只有在很短的距离下才能获得最高速率传输。一般</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">100</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">米长双绞线最大传输速率仅为</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">1Mb/s</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">。</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'"><br/></span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'"><br/></span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">　　</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">RS-485</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">需要</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">2</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">个终接电阻，其阻值要求等于传输电缆的特性阻抗。在矩距离传输时可不需终接电阻，即一般在</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">300</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">米以下不需终接电阻。终接电阻接在传输总线的两端。</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">&nbsp;</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'"><br/></span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'"><br/></span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; FONT-WEIGHT: bold; mso-spacerun: 'yes'"><o:p></o:p></span></p>
<p style="LINE-HEIGHT: 150%; MARGIN-TOP: 0pt; MARGIN-BOTTOM: 0pt" class="p0"><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; FONT-WEIGHT: bold; mso-spacerun: 'yes'">三、关于</span><span style="FONT-FAMILY: 'Times New="New"  Roman'; FONT-SIZE: 12pt; FONT-WEIGHT: bold; mso-spacerun: 'yes'">RS232</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; FONT-WEIGHT: bold; mso-spacerun: 'yes'"><o:p></o:p></span></p>
<p style="LINE-HEIGHT: 150%; MARGIN-TOP: 0pt; MARGIN-BOTTOM: 0pt" class="p0"><span style="FONT-FAMILY: 'Times New="New"  Roman'; FONT-SIZE: 12pt; FONT-WEIGHT: bold; mso-spacerun: 'yes'">&nbsp;&nbsp;&nbsp;&nbsp;</span><span style="FONT-FAMILY: 'Times New="New"  Roman'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">就是串口，电脑机箱后方的<font face="Times New="New"  Roman">9</font><font face="宋体">芯插座，旁边一般有&nbsp;</font><font face="Times New="New"  Roman">"|O|O|"&nbsp;</font><font face="宋体">样标识。&nbsp;</font></span><span style="FONT-FAMILY: 'Times New="New"  Roman'; FONT-SIZE: 12pt; mso-spacerun: 'yes'"><o:p></o:p></span></p>
<p style="LINE-HEIGHT: 150%; MARGIN-TOP: 0pt; MARGIN-BOTTOM: 0pt" class="p0"><span style="FONT-FAMILY: 'Times New="New"  Roman'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">一般机箱有两个，新机箱有可能只有一个。笔记本电脑有可能没有。&nbsp;</span><span style="FONT-FAMILY: 'Times New="New"  Roman'; FONT-SIZE: 12pt; mso-spacerun: 'yes'"><o:p></o:p></span></p>
<p style="LINE-HEIGHT: 150%; MARGIN-TOP: 0pt; MARGIN-BOTTOM: 0pt" class="p0"><span style="FONT-FAMILY: 'Times New="New"  Roman'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">有很多工业仪器将它作为标准通信端口。通信的内容与格式一般附在仪器的用户说明书中。&nbsp;</span><span style="FONT-FAMILY: 'Times New="New"  Roman'; FONT-SIZE: 12pt; mso-spacerun: 'yes'"><o:p></o:p></span></p>
<p style="LINE-HEIGHT: 150%; MARGIN-TOP: 0pt; MARGIN-BOTTOM: 0pt" class="p0"><span style="FONT-FAMILY: 'Times New="New"  Roman'; FONT-SIZE: 12pt; mso-spacerun: 'yes'"><o:p></o:p></span></p>
<p style="LINE-HEIGHT: 150%; MARGIN-TOP: 0pt; TEXT-INDENT: 24pt; MARGIN-BOTTOM: 0pt" class="p0"><span style="FONT-FAMILY: 'Times New="New"  Roman'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">计算机与计算机或计算机与终端之间的数据传送可以采用串行通讯和并行通讯二种方式。由于串行通讯方式具有使用线路少、成本低，特别是在远程传输时，避免了多条线路特性的不一致而被广泛采用。&nbsp;在串行通讯时，要求通讯双方都采用一个标准接口，使不同&nbsp;的设备可以方便地连接起来进行通讯。&nbsp;<font face="Times New="New"  Roman">RS-232-C</font><font face="宋体">接口（又称&nbsp;</font><font face="Times New="New"  Roman">EIA&nbsp;RS-232-C</font><font face="宋体">）是目前最常用的一种串行通讯接口。它是在</font><font face="Times New="New"  Roman">1970</font><font face="宋体">年由美国电子工业协会（</font><font face="Times New="New"  Roman">EIA</font><font face="宋体">）联合贝尔系统、&nbsp;调制解调器厂家及计算机终端生产厂家共同制定的用于串行通讯的标&nbsp;准。它的全名是</font><font face="Times New="New"  Roman">“</font><font face="宋体">数据终端设备（</font><font face="Times New="New"  Roman">DTE</font><font face="宋体">）和数据通讯设备（</font><font face="Times New="New"  Roman">DCE</font><font face="宋体">）之间&nbsp;串行二进制数据交换接口技术标准</font><font face="Times New="New"  Roman">”</font><font face="宋体">该标准规定采用一个</font><font face="Times New="New"  Roman">25</font><font face="宋体">个脚的&nbsp;</font><font face="Times New="New"  Roman">DB25</font><font face="宋体">连接器，对连接器的每个引脚的信号内容加以规定，还对各种信&nbsp;号的电平加以规定。&nbsp;</font></span><span style="FONT-FAMILY: 'Times New="New"  Roman'; FONT-SIZE: 12pt; mso-spacerun: 'yes'"><o:p></o:p></span></p>
<p style="LINE-HEIGHT: 150%; MARGIN-TOP: 0pt; MARGIN-BOTTOM: 0pt" class="p0"><span style="FONT-FAMILY: 'Times New="New"  Roman'; FONT-SIZE: 12pt; mso-spacerun: 'yes'"><o:p></o:p></span></p>
<p style="LINE-HEIGHT: 150%; MARGIN-TOP: 0pt; MARGIN-BOTTOM: 0pt" class="p0"><span style="FONT-FAMILY: 'Times New="New"  Roman'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">（<font face="Times New="New"  Roman">1</font><font face="宋体">）接口的信号内容&nbsp;实际上</font><font face="Times New="New"  Roman">RS-232-C</font><font face="宋体">的</font><font face="Times New="New"  Roman">25</font><font face="宋体">条引线中有许多是很少使用的，在计算机与终端通讯中一般只使用</font><font face="Times New="New"  Roman">3-9</font><font face="宋体">条引线。</font><font face="Times New="New"  Roman">RS-232-C</font><font face="宋体">最常用的</font><font face="Times New="New"  Roman">9</font><font face="宋体">条引线的信号内容见附表</font><font face="Times New="New"  Roman">1</font><font face="宋体">所示&nbsp;</font></span><span style="FONT-FAMILY: 'Times New="New"  Roman'; FONT-SIZE: 12pt; mso-spacerun: 'yes'"><o:p></o:p></span></p>
<p style="LINE-HEIGHT: 150%; MARGIN-TOP: 0pt; MARGIN-BOTTOM: 0pt" class="p0"><span style="FONT-FAMILY: 'Times New="New"  Roman'; FONT-SIZE: 12pt; mso-spacerun: 'yes'"><o:p></o:p></span></p>
<p style="LINE-HEIGHT: 150%; MARGIN-TOP: 0pt; MARGIN-BOTTOM: 0pt" class="p0"><span style="FONT-FAMILY: 'Times New="New"  Roman'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">（<font face="Times New="New"  Roman">2</font><font face="宋体">）接口的电气特性&nbsp;在</font><font face="Times New="New"  Roman">RS-232-C</font><font face="宋体">中任何一条信号线的电压均为负逻辑关系。即：逻&nbsp;辑</font><font face="Times New="New"  Roman">“1”</font><font face="宋体">，</font><font face="Times New="New"  Roman">-5—&nbsp;-15V</font><font face="宋体">；逻辑</font><font face="Times New="New"  Roman">“0”&nbsp;+5—&nbsp;+15V&nbsp;</font><font face="宋体">。噪声容限为</font><font face="Times New="New"  Roman">2V</font><font face="宋体">。即&nbsp;要求接收器能识别低至</font><font face="Times New="New"  Roman">+3V</font><font face="宋体">的信号作为逻辑</font><font face="Times New="New"  Roman">“0”</font><font face="宋体">，高到</font><font face="Times New="New"  Roman">-3V</font><font face="宋体">的信号&nbsp;作为逻辑</font><font face="Times New="New"  Roman">“1”&nbsp;</font></span><span style="FONT-FAMILY: 'Times New="New"  Roman'; FONT-SIZE: 12pt; mso-spacerun: 'yes'"><o:p></o:p></span></p>
<p style="LINE-HEIGHT: 150%; MARGIN-TOP: 0pt; MARGIN-BOTTOM: 0pt" class="p0"><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'"><o:p></o:p></span></p>
<p style="LINE-HEIGHT: 150%; MARGIN-TOP: 0pt; TEXT-INDENT: 6pt; MARGIN-BOTTOM: 0pt" class="p0"><span style="FONT-FAMILY: 'Times New="New"  Roman'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">(3)&nbsp;<font face="宋体">接口的物理结构&nbsp;</font><font face="Times New="New"  Roman">RS-232-C</font><font face="宋体">接口连接器一般使用型号为</font><font face="Times New="New"  Roman">DB-25</font><font face="宋体">的</font><font face="Times New="New"  Roman">25</font><font face="宋体">芯插头座</font><font face="Times New="New"  Roman">,</font><font face="宋体">通常插头在</font><font face="Times New="New"  Roman">DCE</font><font face="宋体">端</font><font face="Times New="New"  Roman">,</font><font face="宋体">插座在</font><font face="Times New="New"  Roman">DTE</font><font face="宋体">端</font><font face="Times New="New"  Roman">.&nbsp;</font><font face="宋体">一些设备与</font><font face="Times New="New"  Roman">PC</font><font face="宋体">机连接的</font><font face="Times New="New"  Roman">RS-232-C</font><font face="宋体">接口</font><font face="Times New="New"  Roman">,</font><font face="宋体">因为不使用对方的传送控制信号</font><font face="Times New="New"  Roman">,</font><font face="宋体">只需三条接口线</font><font face="Times New="New"  Roman">,</font><font face="宋体">即</font><font face="Times New="New"  Roman">“</font><font face="宋体">发送数据</font><font face="Times New="New"  Roman">”</font><font face="宋体">、</font><font face="Times New="New"  Roman">“</font><font face="宋体">接收数据</font><font face="Times New="New"  Roman">”</font><font face="宋体">和</font><font face="Times New="New"  Roman">“</font><font face="宋体">信号地</font><font face="Times New="New"  Roman">”</font><font face="宋体">。所以采用</font><font face="Times New="New"  Roman">DB-9</font><font face="宋体">的</font><font face="Times New="New"  Roman">9</font><font face="宋体">芯插头座，传输线采用屏蔽双绞线。&nbsp;</font></span><span style="FONT-FAMILY: 'Times New="New"  Roman'; FONT-SIZE: 12pt; mso-spacerun: 'yes'"><o:p></o:p></span></p>
<p style="LINE-HEIGHT: 150%; MARGIN-TOP: 0pt; MARGIN-BOTTOM: 0pt" class="p0"><span style="FONT-FAMILY: 'Times New="New"  Roman'; FONT-SIZE: 12pt; mso-spacerun: 'yes'"><o:p></o:p></span></p>
<p style="LINE-HEIGHT: 150%; MARGIN-TOP: 0pt; MARGIN-BOTTOM: 0pt" class="p0"><span style="FONT-FAMILY: 'Times New="New"  Roman'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">（<font face="Times New="New"  Roman">4</font><font face="宋体">）传输电缆长度&nbsp;由</font><font face="Times New="New"  Roman">RS-232C</font><font face="宋体">标准规定在码元畸变小于</font><font face="Times New="New"  Roman">4%</font><font face="宋体">的情况下，传输电缆长度应为</font><font face="Times New="New"  Roman">50</font><font face="宋体">英尺，其实这个</font><font face="Times New="New"  Roman">4%</font><font face="宋体">的码元畸变是很保守的，在实际应用中，约有</font><font face="Times New="New"  Roman">99%</font><font face="宋体">的用户是按码元畸变</font><font face="Times New="New"  Roman">10-20%</font><font face="宋体">的范围工作的，所以实际使用中最大距离会远超过</font><font face="Times New="New"  Roman">50</font><font face="宋体">英尺，美国</font><font face="Times New="New"  Roman">DEC</font><font face="宋体">公司曾规定允许码元畸变为</font><font face="Times New="New"  Roman">10%</font><font face="宋体">而得出附表</font><font face="Times New="New"  Roman">2&nbsp;</font><font face="宋体">的实验结果。其中</font><font face="Times New="New"  Roman">1</font><font face="宋体">号电缆为屏蔽电缆，型号为</font><font face="Times New="New"  Roman">DECP.NO.9107723&nbsp;</font><font face="宋体">内有三对双绞线，每对由</font><font face="Times New="New"  Roman">22#&nbsp;AWG&nbsp;</font><font face="宋体">组成，其外覆以屏蔽网。</font><font face="Times New="New"  Roman">2</font><font face="宋体">号电缆为不带屏蔽的电缆。型号为</font><font face="Times New="New"  Roman">DECP.NO.9105856-04</font><font face="宋体">是</font><font face="Times New="New"  Roman">22#AWG</font><font face="宋体">的四芯电缆。</font></span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'"><o:p></o:p></span></p>
<p style="LINE-HEIGHT: 150%; MARGIN-TOP: 0pt; MARGIN-BOTTOM: 0pt" class="p0"><span style="FONT-FAMILY: 'Times New="New"  Roman'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">串行通讯</span><span style="FONT-FAMILY: 'Times New="New"  Roman'; FONT-SIZE: 12pt; mso-spacerun: 'yes'"><o:p></o:p></span></p>
<p style="LINE-HEIGHT: 150%; MARGIN-TOP: 0pt; MARGIN-BOTTOM: 0pt" class="p0"><span style="FONT-FAMILY: 'Times New="New"  Roman'; FONT-SIZE: 12pt; FONT-WEIGHT: bold; mso-spacerun: 'yes'"><o:p></o:p></span></p>
<p style="LINE-HEIGHT: 150%; MARGIN-TOP: 0pt; MARGIN-BOTTOM: 0pt" class="p0"><span style="FONT-FAMILY: 'Times New="New"  Roman'; FONT-SIZE: 12pt; FONT-WEIGHT: bold; mso-spacerun: 'yes'">　　一条信息的各位数据被逐位按顺序传送的通讯方式称为串行通讯</span><span style="FONT-FAMILY: 'Times New="New"  Roman'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">。串行通讯的特点是：数据位传送，传按位顺序进行，最少只需一根传输线即可完成，成本低但送速度慢。串行通讯的距离可以从几米到几千米。&nbsp;根据信息的传送方向，串行通讯可以进一步分为</span><span style="FONT-FAMILY: 'Times New="New"  Roman'; FONT-SIZE: 12pt; FONT-WEIGHT: bold; mso-spacerun: 'yes'">单工、半双工和全双工</span><span style="FONT-FAMILY: 'Times New="New"  Roman'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">三种。信息只能单向传送为单工；信息能双向传送但不能同时双向传送称为半双工；信息能够同时双向传送则称为全双工。&nbsp;串行通讯又分为异步通讯和同步通讯两种方式。在单片机中，主要使用异步通讯方式。</span><span style="FONT-FAMILY: 'Times New="New"  Roman'; FONT-SIZE: 12pt; mso-spacerun: 'yes'"><o:p></o:p></span></p>
<p style="LINE-HEIGHT: 150%; MARGIN-TOP: 0pt; MARGIN-BOTTOM: 0pt" class="p0"><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'"><o:p></o:p></span></p>
<p style="LINE-HEIGHT: 150%; MARGIN-TOP: 0pt; MARGIN-BOTTOM: 0pt" class="p0"><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; FONT-WEIGHT: bold; mso-spacerun: 'yes'">四、关于RS458</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; FONT-WEIGHT: bold; mso-spacerun: 'yes'"><o:p></o:p></span></p>
<p style="LINE-HEIGHT: 150%; MARGIN-TOP: 0pt; MARGIN-BOTTOM: 0pt" class="p0"><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">（一）</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">布线规范</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'"><br/></span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">1、&nbsp;控制器通讯线（包括485/422、232和韦根等通讯线）必须采用国际通用的8芯屏蔽双绞线,这样可有效防止和屏蔽干扰。线径大于0.3mm总线长度不超过1200建议在1000米以内，如果更长请选用其它专用485/232转换器或者加中继器，并选用更粗的通讯电缆。</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'"><br/></span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">2、&nbsp;&nbsp;</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'">控制器GND&nbsp;485-&nbsp;485＋分别对应连接485转换器GND&nbsp;TD(A)&nbsp;TD(B)，通讯线路采用串联挂接式连接，请勿采用星型连接或者局部星型连接（如图二）。如果线路过长和设备过多，请在最后一台设备上增加终端电阻（有跳线加载）总线最多可挂接128台控制器。</span><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'"><o:p></o:p></span></p>
<p style="LINE-HEIGHT: 150%; MARGIN-TOP: 0pt; MARGIN-BOTTOM: 0pt" class="p0"><span style="FONT-FAMILY: '宋体'; FONT-SIZE: 12pt; mso-spacerun: 'yes'"></span>&nbsp;</p><!--EndFragment-->

&nbsp;学习了，谢谢！！！

<p>很有用的文档</p>
<p>&nbsp; 谢谢</p>
<p>&nbsp;</p>