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标题:
[原创]485总线通讯方法解析
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作者:
bjmonsoon
时间:
2008-4-13 21:44
标题:
[原创]485总线通讯方法解析
<p class="MsoNormal" align="left" style="MARGIN: 0cm 0cm 7.5pt; WORD-BREAK: break-all; LINE-HEIGHT: 18pt; TEXT-ALIGN: left; mso-pagination: widow-orphan;"><span lang="EN-US" style="FONT-FAMILY: 宋体; mso-bidi-font-size: 10.5pt; mso-font-kerning: 0pt; mso-bidi-font-family: Arial;"> 1</span><span style="FONT-FAMILY: 宋体; mso-bidi-font-size: 10.5pt; mso-font-kerning: 0pt; mso-bidi-font-family: Arial;">。<span lang="EN-US">485</span>总线应采用什么样的通讯线？一条总线上可以挂接多少台设备？<span lang="EN-US"><p></p></span></span></p><p class="MsoNormal" align="left" style="MARGIN: 3pt 0cm 7.5pt; WORD-BREAK: break-all; LINE-HEIGHT: 18pt; TEXT-ALIGN: left; mso-pagination: widow-orphan;"><span lang="EN-US" style="FONT-FAMILY: 宋体; mso-bidi-font-size: 10.5pt; mso-font-kerning: 0pt; mso-bidi-font-family: Arial;"> </span><span style="FONT-FAMILY: 宋体; mso-bidi-font-size: 10.5pt; mso-font-kerning: 0pt; mso-bidi-font-family: Arial;">必须采用<span lang="EN-US">RVSP</span>屏蔽双绞线。所用屏蔽双绞线规格，与<span lang="EN-US">485</span>通讯线的距离和挂接的设备数量有关，如下表所示。采用屏蔽双绞线有助于减少和消除两根<span lang="EN-US">485</span>通信线之间产生的分布电容以及来自于通讯线周围产生的共模干扰。 通讯距离 设备数量 通讯线规格<span lang="EN-US"> 1<chmetcnv wst="on" unitname="m" sourcevalue="400" hasspace="False" negative="True" numbertype="1" tcsc="0">-400m</chmetcnv> 1 - 32 </span>台<span lang="EN-US">
<chmetcnv wst="on" unitname="mm" sourcevalue=".5" hasspace="False" negative="False" numbertype="1" tcsc="0">0.5mm</chmetcnv>2 400<chmetcnv wst="on" unitname="m" sourcevalue="800" hasspace="False" negative="True" numbertype="1" tcsc="0">-800m</chmetcnv> 1 - 16 </span>台<span lang="EN-US">
<chmetcnv wst="on" unitname="mm" sourcevalue=".5" hasspace="False" negative="False" numbertype="1" tcsc="0">0.5mm</chmetcnv>2 400<chmetcnv wst="on" unitname="m" sourcevalue="800" hasspace="False" negative="True" numbertype="1" tcsc="0">-800m</chmetcnv> 17 - 32 </span>台<span lang="EN-US">
<chmetcnv wst="on" unitname="mm" sourcevalue=".75" hasspace="False" negative="False" numbertype="1" tcsc="0">0.75mm</chmetcnv>2 800<chmetcnv wst="on" unitname="m" sourcevalue="1200" hasspace="False" negative="True" numbertype="1" tcsc="0">-1200m</chmetcnv> 1 - 8 </span>台<span lang="EN-US">
<chmetcnv wst="on" unitname="mm" sourcevalue=".5" hasspace="False" negative="False" numbertype="1" tcsc="0">0.5mm</chmetcnv>2 800<chmetcnv wst="on" unitname="m" sourcevalue="1200" hasspace="False" negative="True" numbertype="1" tcsc="0">-1200m</chmetcnv> 9 - 21 </span>台<span lang="EN-US">
<chmetcnv wst="on" unitname="mm" sourcevalue=".75" hasspace="False" negative="False" numbertype="1" tcsc="0">0.75mm</chmetcnv>2 800<chmetcnv wst="on" unitname="m" sourcevalue="1200" hasspace="False" negative="True" numbertype="1" tcsc="0">-1200m</chmetcnv> 22 - 32</span>台<span lang="EN-US">
<chmetcnv wst="on" unitname="mm" sourcevalue="1" hasspace="False" negative="False" numbertype="1" tcsc="0">1.0mm</chmetcnv>2 </span>工程商大都习惯采用<span lang="EN-US">5</span>类网线或超<span lang="EN-US">5</span>类网线作为<span lang="EN-US">485</span>通信线，这是错误的。这是因为：（<span lang="EN-US">1</span>） 普通网线没有屏蔽层，不能防止共模干扰。（<span lang="EN-US">2</span>）网线只有<chmetcnv wst="on" unitname="mm" sourcevalue=".2" hasspace="False" negative="False" numbertype="1" tcsc="0"><span lang="EN-US">0.2mm</span></chmetcnv>平方，线径太细，会导致传输距离降低和可挂接的设备减少。（<span lang="EN-US">3</span>）网络线为单股的铜线，相比多芯线而言容易断裂。<span lang="EN-US">
<p></p></span></span></p><p class="MsoNormal" align="left" style="MARGIN: 3pt 0cm 7.5pt; WORD-BREAK: break-all; LINE-HEIGHT: 18pt; TEXT-ALIGN: left; mso-pagination: widow-orphan;"><span lang="EN-US" style="FONT-FAMILY: 宋体; mso-bidi-font-size: 10.5pt; mso-font-kerning: 0pt; mso-bidi-font-family: Arial;">2</span><span style="FONT-FAMILY: 宋体; mso-bidi-font-size: 10.5pt; mso-font-kerning: 0pt; mso-bidi-font-family: Arial;">。 为什么要接地<span lang="EN-US">
<p></p></span></span></p><p class="MsoNormal" align="left" style="MARGIN: 3pt 0cm 7.5pt; WORD-BREAK: break-all; LINE-HEIGHT: 18pt; TEXT-ALIGN: left; mso-pagination: widow-orphan;"><span lang="EN-US" style="FONT-FAMILY: 宋体; mso-bidi-font-size: 10.5pt; mso-font-kerning: 0pt; mso-bidi-font-family: Arial;">485</span><span style="FONT-FAMILY: 宋体; mso-bidi-font-size: 10.5pt; mso-font-kerning: 0pt; mso-bidi-font-family: Arial;">收发器在规定的共模电压<span lang="EN-US">-7V</span>至<span lang="EN-US">+12V</span>之间时，才能正常工作。如果超出此范围会影响通讯，严重的会损坏通讯接口。共模干扰会增大上述共模电压。消除共模干扰的有效手段之一是将<span lang="EN-US">485</span>通讯线的屏蔽层用作地线，将机具、电脑等网络中的设备地连接在一起，并由一点可靠地接入大地。<span lang="EN-US"><p></p></span></span></p><p class="MsoNormal" align="left" style="MARGIN: 0cm 0cm 7.5pt; WORD-BREAK: break-all; LINE-HEIGHT: 18pt; TEXT-ALIGN: left; mso-pagination: widow-orphan;"><span lang="EN-US" style="FONT-FAMILY: 宋体; mso-bidi-font-size: 10.5pt; mso-font-kerning: 0pt; mso-bidi-font-family: Arial;">3</span><span style="FONT-FAMILY: 宋体; mso-bidi-font-size: 10.5pt; mso-font-kerning: 0pt; mso-bidi-font-family: Arial;">。 电控锁和控制器<span lang="EN-US">/</span>读卡器可以用同一个电源共电吗？<span lang="EN-US"><p></p></span></span></p><p class="MsoNormal" align="left" style="MARGIN: 3pt 0cm 7.5pt; WORD-BREAK: break-all; LINE-HEIGHT: 18pt; TEXT-ALIGN: left; mso-pagination: widow-orphan;"><span lang="EN-US" style="FONT-FAMILY: 宋体; mso-bidi-font-size: 10.5pt; mso-font-kerning: 0pt; mso-bidi-font-family: Arial;"> </span><span style="FONT-FAMILY: 宋体; mso-bidi-font-size: 10.5pt; mso-font-kerning: 0pt; mso-bidi-font-family: Arial;">不能。在电控锁不动作的情况下，<span lang="EN-US">SKPS</span>的纹波电压只有<span lang="EN-US">40-50mV</span>； 一旦动作，即在电控锁在开门和关门时，纹波电压会上升到<span lang="EN-US">100mV-300mV</span>，该纹波会通过地线进入控制器和读卡器，导致通讯芯片和<span lang="EN-US">CPU</span>发热，导致通讯不稳，严重的还会烧毁芯片。而且电控锁在断电和上电的瞬间，电控锁里面的线圈，会充放电产生一个高达<span lang="EN-US">850mA</span>的脉冲，如果电控锁的两端没有并联二极管的话，该纹波信号也会传入控制器和读卡器。推荐一个控制器和它下面挂接的所有读卡器共用一个<span lang="EN-US">SKPS</span>电源；该控制器下面每个电控锁各使用一个单独的<span lang="EN-US">SKPS</span>电源。<span lang="EN-US"><p></p></span></span></p><p class="MsoNormal" align="left" style="MARGIN: 3pt 0cm 7.5pt; WORD-BREAK: break-all; LINE-HEIGHT: 18pt; TEXT-ALIGN: left; mso-pagination: widow-orphan;"><span lang="EN-US" style="FONT-FAMILY: 宋体; mso-bidi-font-size: 10.5pt; mso-font-kerning: 0pt; mso-bidi-font-family: Arial;"> 4</span><span style="FONT-FAMILY: 宋体; mso-bidi-font-size: 10.5pt; mso-font-kerning: 0pt; mso-bidi-font-family: Arial;">。<span lang="EN-US">485</span>通信线应如何走线？<span lang="EN-US">
<p></p></span></span></p><p class="MsoNormal" align="left" style="MARGIN: 3pt 0cm 7.5pt; WORD-BREAK: break-all; LINE-HEIGHT: 18pt; TEXT-ALIGN: left; mso-pagination: widow-orphan;"><span style="FONT-FAMILY: 宋体; mso-bidi-font-size: 10.5pt; mso-font-kerning: 0pt; mso-bidi-font-family: Arial;">通信线尽量远离高压电线，不要与电源线并行，更不能捆扎在一起。<span lang="EN-US">
<p></p></span></span></p><p class="MsoNormal" align="left" style="MARGIN: 3pt 0cm 7.5pt; WORD-BREAK: break-all; LINE-HEIGHT: 18pt; TEXT-ALIGN: left; mso-pagination: widow-orphan;"><span lang="EN-US" style="FONT-FAMILY: 宋体; mso-bidi-font-size: 10.5pt; mso-font-kerning: 0pt; mso-bidi-font-family: Arial;">5</span><span style="FONT-FAMILY: 宋体; mso-bidi-font-size: 10.5pt; mso-font-kerning: 0pt; mso-bidi-font-family: Arial;">。为什么<span lang="EN-US">485</span>总线要采用手拉手结构，而不能采用星形结构？<span lang="EN-US">
<p></p></span></span></p><p class="MsoNormal" align="left" style="MARGIN: 3pt 0cm 7.5pt; WORD-BREAK: break-all; LINE-HEIGHT: 18pt; TEXT-ALIGN: left; mso-pagination: widow-orphan;"><span style="FONT-FAMILY: 宋体; mso-bidi-font-size: 10.5pt; mso-font-kerning: 0pt; mso-bidi-font-family: Arial;">星形结构会产生反射信号，从而影响到<span lang="EN-US">485</span>通信。总线到每个终端设备的分支线长度应尽量短，一般不要超出<chmetcnv wst="on" unitname="米" sourcevalue="5" hasspace="False" negative="False" numbertype="1" tcsc="0"><span lang="EN-US">5</span>米</chmetcnv>。分支线如果没有接终端，会有反射信号，对通讯产生较强的干扰，应将其去掉。门禁系统中，有两个地方应用到<span lang="EN-US">485</span>总线。一是计算机到下面挂接的控制器，二是控制器到下面挂接的<span lang="EN-US">485</span>读卡器。<span lang="EN-US"><p></p></span></span></p><p class="MsoNormal" align="left" style="MARGIN: 3pt 0cm 7.5pt; WORD-BREAK: break-all; LINE-HEIGHT: 18pt; TEXT-ALIGN: left; mso-pagination: widow-orphan;"><span lang="EN-US" style="FONT-FAMILY: 宋体; mso-bidi-font-size: 10.5pt; mso-font-kerning: 0pt; mso-bidi-font-family: Arial;"> 6</span><span style="FONT-FAMILY: 宋体; mso-bidi-font-size: 10.5pt; mso-font-kerning: 0pt; mso-bidi-font-family: Arial;">。<span lang="EN-US">485</span>总线上设备到设备之间可以有接点吗？<span lang="EN-US"><p></p></span></span></p><p class="MsoNormal" align="left" style="MARGIN: 3pt 0cm 7.5pt; WORD-BREAK: break-all; LINE-HEIGHT: 18pt; TEXT-ALIGN: left; mso-pagination: widow-orphan;"><span lang="EN-US" style="FONT-FAMILY: 宋体; mso-bidi-font-size: 10.5pt; mso-font-kerning: 0pt; mso-bidi-font-family: Arial;"> </span><span style="FONT-FAMILY: 宋体; mso-bidi-font-size: 10.5pt; mso-font-kerning: 0pt; mso-bidi-font-family: Arial;">在同一个网络系统中，使用同一种电缆，尽量减少线路中的接点。接点处确保焊接良好，包扎紧密，避免松动和氧化。保证一条单一的、连续的信号通道作为总线。<span lang="EN-US">
<p></p></span></span></p><p class="MsoNormal" align="left" style="MARGIN: 3pt 0cm 7.5pt; WORD-BREAK: break-all; LINE-HEIGHT: 18pt; TEXT-ALIGN: left; mso-pagination: widow-orphan;"><span lang="EN-US" style="FONT-FAMILY: 宋体; mso-bidi-font-size: 10.5pt; mso-font-kerning: 0pt; mso-bidi-font-family: Arial;">7</span><span style="FONT-FAMILY: 宋体; mso-bidi-font-size: 10.5pt; mso-font-kerning: 0pt; mso-bidi-font-family: Arial;">。什么叫共模干扰和差模干扰？如何消除通讯线上的干扰？<span lang="EN-US"><p></p></span></span></p><p class="MsoNormal" align="left" style="MARGIN: 3pt 0cm 7.5pt; WORD-BREAK: break-all; LINE-HEIGHT: 18pt; TEXT-ALIGN: left; mso-pagination: widow-orphan;"><span lang="EN-US" style="FONT-FAMILY: 宋体; mso-bidi-font-size: 10.5pt; mso-font-kerning: 0pt; mso-bidi-font-family: Arial;"> 485</span><span style="FONT-FAMILY: 宋体; mso-bidi-font-size: 10.5pt; mso-font-kerning: 0pt; mso-bidi-font-family: Arial;">通信线由两根双绞的线组成，它是通过两根通信线之间的电压差的方式来传递信号，因此称之为差分电压传输。差模干扰在两根信号线之间传输，属于对称性干扰。消除差模干扰的方法是在电路中增加一个偏值电阻<span lang="EN-US">,</span>并采用双绞线； 共模干扰是在信号线与地之间传输，属于非对称性干扰。消除共模干扰的方法包括：（<span lang="EN-US">1</span>）采用屏蔽双绞线并有效接地（<span lang="EN-US">2</span>）强电场的地方还要考虑采用镀锌管屏蔽（<span lang="EN-US">3</span>）布线时远离高压线，更不能将高压电源线和信号线捆在一起走线（<span lang="EN-US">4</span>）不要和电控锁共用同一个电源（<span lang="EN-US">5</span>）采用线性稳压电源或高品质的开关电源<span lang="EN-US">(</span>纹波干扰小于<span lang="EN-US">50mV) <p></p></span></span></p><p class="MsoNormal" align="left" style="MARGIN: 3pt 0cm 7.5pt; WORD-BREAK: break-all; LINE-HEIGHT: 18pt; TEXT-ALIGN: left; mso-pagination: widow-orphan;"><span lang="EN-US" style="FONT-FAMILY: 宋体; mso-bidi-font-size: 10.5pt; mso-font-kerning: 0pt; mso-bidi-font-family: Arial;">8</span><span style="FONT-FAMILY: 宋体; mso-bidi-font-size: 10.5pt; mso-font-kerning: 0pt; mso-bidi-font-family: Arial;">。什么情况下在<span lang="EN-US">485</span>总线上要增加终端电阻？<span lang="EN-US"><p></p></span></span></p><p class="MsoNormal" align="left" style="MARGIN: 3pt 0cm 7.5pt; WORD-BREAK: break-all; LINE-HEIGHT: 18pt; TEXT-ALIGN: left; mso-pagination: widow-orphan;"><span lang="EN-US" style="FONT-FAMILY: 宋体; mso-bidi-font-size: 10.5pt; mso-font-kerning: 0pt; mso-bidi-font-family: Arial;"> </span><span style="FONT-FAMILY: 宋体; mso-bidi-font-size: 10.5pt; mso-font-kerning: 0pt; mso-bidi-font-family: Arial;">一般情况下不需要增加终端电阻，只有在<span lang="EN-US">485</span>通信距离超过<chmetcnv wst="on" unitname="米" sourcevalue="300" hasspace="False" negative="False" numbertype="1" tcsc="0"><span lang="EN-US">300</span>米</chmetcnv>的情况下，要在<span lang="EN-US">485</span>通讯的开始端和结束端增加终端电阻。尤其是<span lang="EN-US">485</span>总线上设备数量较少时。当设备数量较多时（如超过<span lang="EN-US">22</span>台）。一般不需增加终端电阻，因为终端电阻会降低<span lang="EN-US">485</span>总线的负载能力。当需要增加终端电阻时，只要将控制器上面的终端电阻跳线置位既可，如果另一端连接的是计算机的话，同时将<span lang="EN-US">485</span>转换器的棕色和白色短路。<span lang="EN-US">
<p></p></span></span></p><p class="MsoNormal" align="left" style="MARGIN: 3pt 0cm 7.5pt; WORD-BREAK: break-all; LINE-HEIGHT: 18pt; TEXT-ALIGN: left; mso-pagination: widow-orphan;"><span lang="EN-US" style="FONT-FAMILY: 宋体; mso-bidi-font-size: 10.5pt; mso-font-kerning: 0pt; mso-bidi-font-family: Arial;">9</span><span style="FONT-FAMILY: 宋体; mso-bidi-font-size: 10.5pt; mso-font-kerning: 0pt; mso-bidi-font-family: Arial;">。如何延长<span lang="EN-US">485</span>的通讯距离<span lang="EN-US"><p></p></span></span></p><p class="MsoNormal" align="left" style="MARGIN: 3pt 0cm 7.5pt; WORD-BREAK: break-all; LINE-HEIGHT: 18pt; TEXT-ALIGN: left; mso-pagination: widow-orphan;"><span lang="EN-US" style="FONT-FAMILY: 宋体; mso-bidi-font-size: 10.5pt; mso-font-kerning: 0pt; mso-bidi-font-family: Arial;"> 485</span><span style="FONT-FAMILY: 宋体; mso-bidi-font-size: 10.5pt; mso-font-kerning: 0pt; mso-bidi-font-family: Arial;">网络的规范之一是<span lang="EN-US">1.2</span>公里长度，<span lang="EN-US">32</span>个节点数。如果超出了这个限制，那么必须采用<span lang="EN-US">485</span>集线器来拓展网络距离或节点数。 利用<span lang="EN-US">485</span>集线器，可以将一个大型<span lang="EN-US">485</span>网络分隔成若干个网段。<span lang="EN-US">485</span>集线器就如同<span lang="EN-US">485</span>网段之间连接的<span lang="EN-US">"</span>桥梁<span lang="EN-US">"</span>。当然每个网段还是遵循上面的<span lang="EN-US">485</span>规范，即<span lang="EN-US">1.2</span>公里长度，<span lang="EN-US">32</span>个节点数。 利用<span lang="EN-US">485</span>集线器延长网络距离图示： 利用<span lang="EN-US">485</span>集线器解决<span lang="EN-US">485</span>分叉问题，如图所示： 利用<span lang="EN-US">485</span>集线器构造星型<span lang="EN-US">485</span>网络<span lang="EN-US"> 485</span>集线器是<span lang="EN-US">485</span>中继器概念的拓广，它不仅解决了多分叉问题，同时也解决了网段之间相互隔离的问题，即某一个网段出现问题（例如短路等），不至于影响到其它网段，从而极大地提高了大型网络的安全性和稳定性。我们可以从局域网从总线型到星型的发展历程，来体会星型布线网络给我们带来的好处。同样，采用<span lang="EN-US">485</span>集线器构成的星型<span lang="EN-US">485</span>网络也将是<span lang="EN-US">485</span>网络发展的一个方向。<span lang="EN-US"><p></p></span></span></p>
作者:
无剑
时间:
2008-4-14 10:25
你在这看到哪写出的
作者:
乐得安
时间:
2008-4-20 20:29
<p>顶上来啊</p><p></p>
作者:
xdzjwyh
时间:
2008-4-21 18:46
顶一下
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