windowsce_net 420串口驱动分析(1)--jesse.htm

WinCE下串口编程应用实例

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                  <P class=MsoBodyText><SPAN 
                  style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">也就是说在原</SPAN><SPAN 
                  lang=EN-US>3wire</SPAN><SPAN 
                  style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">的基础上增加了</SPAN><SPAN 
                  lang=EN-US>DCD,DTR,DSR,RTS,CTS,DELL</SPAN><SPAN 
                  style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">六个控制线。其中</SPAN><SPAN 
                  lang=EN-US style="COLOR: black">RTS/CTS</SPAN><SPAN 
                  style="COLOR: black; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">用于流控制，另外的</SPAN><SPAN 
                  lang=EN-US style="COLOR: black">DCD</SPAN><SPAN 
                  style="COLOR: black; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">和</SPAN><SPAN 
                  lang=EN-US style="COLOR: black">DELL</SPAN><SPAN 
                  style="COLOR: black; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">则留作连接</SPAN><SPAN 
                  lang=EN-US style="COLOR: black">modem</SPAN><SPAN 
                  style="COLOR: black; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">使用。有了专门的硬件流控制引脚也就使得流控制成为可能，以完成收发两端的匹配使得数据可以可靠的传输。用</SPAN><SPAN 
                  lang=EN-US style="COLOR: black">RTS/CTS</SPAN><SPAN 
                  style="COLOR: black; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">（请求发送</SPAN><SPAN 
                  lang=EN-US style="COLOR: black">/</SPAN><SPAN 
                  style="COLOR: black; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">清除发送）流控制时，应将通讯两端的</SPAN><SPAN 
                  lang=EN-US style="COLOR: black">RTS</SPAN><SPAN 
                  style="COLOR: black; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">、</SPAN><SPAN 
                  lang=EN-US style="COLOR: black">CTS</SPAN><SPAN 
                  style="COLOR: black; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">线对应相连</SPAN><SPAN 
                  lang=EN-US style="COLOR: black">).</SPAN><SPAN 
                  style="COLOR: black; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">在发送端准备发送数据之前设置</SPAN><SPAN 
                  lang=EN-US style="COLOR: black">RTS(</SPAN><SPAN class=p><SPAN 
                  lang=EN-US style="COLOR: #006666">Request to 
                  send</SPAN></SPAN><SPAN lang=EN-US 
                  style="COLOR: black">)</SPAN><SPAN 
                  style="COLOR: black; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">也就使发送请求线，若接收端以作好接收准备，就启动响应的</SPAN><SPAN 
                  lang=EN-US style="COLOR: black">CTS</SPAN><SPAN 
                  style="COLOR: black; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">（</SPAN><SPAN 
                  lang=EN-US style="COLOR: black">Clear to send</SPAN><SPAN 
                  style="COLOR: black; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">）引线。这样，收发双发就进入数据传输状态，在此过程中如若接收端处理数据的速度低于发送端的发送速度，接收一端还可以设置</SPAN><SPAN 
                  lang=EN-US style="COLOR: black">CTS</SPAN><SPAN 
                  style="COLOR: black; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">引线恢复原来阻塞得状态以暂时中断数据传输，之后若需要恢复数据传输恢复</SPAN><SPAN 
                  lang=EN-US style="COLOR: black">CTS</SPAN><SPAN 
                  style="COLOR: black; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">状态即可。这样</SPAN><SPAN 
                  lang=EN-US style="COLOR: black">UART</SPAN><SPAN 
                  style="COLOR: black; FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">的传输即实现了流控制，保障了数据传输的完备性。</SPAN><SPAN 
                  lang=EN-US style="COLOR: black"><O:P></O:P></SPAN> </P>
                  <P class=MsoBodyText><SPAN 
                  style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">在这里还要说一下软件流控制，虽然硬件已经可以完成流控制的任务但很多少时候受到连线数的限制不能使用硬件流控制也就设计了专门的软件流控制的方法。现在回到</SPAN><SPAN 
                  lang=EN-US>3</SPAN><SPAN 
                  style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">线传输的情景，若接收端接收数据过程中缓冲器的负载到达某一限制</SPAN><SPAN 
                  lang=EN-US>(</SPAN><SPAN 
                  style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">也就是留出一定的缓冲空间</SPAN><SPAN 
                  lang=EN-US>)</SPAN><SPAN 
                  style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">时接收端向发送端发送一个特殊的标示位</SPAN><SPAN 
                  lang=EN-US>(</SPAN><SPAN 
                  style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">接收停止位</SPAN><SPAN 
                  lang=EN-US>)</SPAN><SPAN 
                  style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">，当发送端收到该标示的时候就停止发送，直到接收端缓冲器低于另一限制后发送标示</SPAN><SPAN 
                  lang=EN-US>(</SPAN><SPAN 
                  style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">接收许可位</SPAN><SPAN 
                  lang=EN-US>)</SPAN><SPAN 
                  style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">给发送端，这样就可以控制数据流的传输起停。这种软件流控制是在给缓冲器留余量来完成的，在收发双端处理器速度差很大的时候就不太适用了，就必须要用硬件流控制。</SPAN> 
                  <BR><BR><SPAN 
                  style="FONT-SIZE: 10pt; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'; mso-bidi-font-family: 'Times New Roman'; mso-bidi-language: HE">其他几个引脚都是与</SPAN><SPAN 
                  lang=EN-US 
                  style="FONT-SIZE: 10pt; FONT-FAMILY: 'Times New Roman'; mso-bidi-language: HE">modem</SPAN><SPAN 
                  style="FONT-SIZE: 10pt; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'; mso-bidi-font-family: 'Times New Roman'; mso-bidi-language: HE">相关的，</SPAN><SPAN 
                  lang=EN-US