📄 ——单片机系统在测控领域的稳定性探讨.htm
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<TD align=middle height=31><FONT size=4><B>单片机系统在测控领域的稳定性探讨
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<TD align=middle height=15>文章作者：中国人民解放军炮兵学院 王占操 曹燕<BR>文章类型：设计应用
文章加入时间：2003年3月27日14:59</TD></TR>
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<TD align=right><FONT color=#cc0000>文章出处：21IC中国电子网</FONT> </TD></TR>
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<P class=MsoNormal style="TEXT-INDENT: 21.75pt"><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">近年来单片机系统在工业测控领域的应用越来越广泛，而对于环境恶劣的工业现场，这种新型的微控制器的可靠性，安全性就成为了一个大的问题。在实验室运行正常的程序到了工业现场却不能运行，或者出现运行不稳定经常死机等。在这里我们主要讨论一下如何通过软件技术来增强系统的稳定运行。</SPAN></P>
<P class=MsoNormal style="TEXT-INDENT: 21.75pt"><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">当系统的</SPAN><SPAN
lang=EN-US>CPU</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">部位受到干扰信号的作用时，将使系统失控。最典型的故障是破坏程序计数器</SPAN><SPAN
lang=EN-US>PC</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">的状态值。导致程序在地址空间内“乱飞”，或者陷入死循环。而我们对这种情况的处理主要有这么几种方法：</SPAN></P>
<P class=MsoNormal
style="MARGIN-LEFT: 39.75pt; TEXT-INDENT: -18pt; mso-list: l0 level1 lfo1; tab-stops: list 39.75pt"><SPAN
lang=EN-US>1、<SPAN style="FONT: 7pt 'Times New Roman'">
</SPAN></SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">指令冗余技术；</SPAN></P>
<P class=MsoNormal
style="MARGIN-LEFT: 39.75pt; TEXT-INDENT: -18pt; mso-list: l0 level1 lfo1; tab-stops: list 39.75pt"><SPAN
lang=EN-US>2、<SPAN style="FONT: 7pt 'Times New Roman'">
</SPAN></SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">软件陷阱技术；</SPAN></P>
<P class=MsoNormal
style="MARGIN-LEFT: 39.75pt; TEXT-INDENT: -18pt; mso-list: l0 level1 lfo1; tab-stops: list 39.75pt"><SPAN
lang=EN-US>3、<SPAN style="FONT: 7pt 'Times New Roman'">
</SPAN></SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">看门狗技术。</SPAN></P>
<P class=MsoNormal style="MARGIN-LEFT: 21.75pt"><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">我们以</SPAN><SPAN
lang=EN-US>MCS-51</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">单片机来做以说明。</SPAN></P>
<P class=MsoNormal><B><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">一、指令冗余技术</SPAN><SPAN
lang=EN-US><o:p></o:p></SPAN></B></P>
<P class=MsoNormal style="TEXT-INDENT: 21.75pt"><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">我们知道，指令由操作码和操作数组成，操作码指明</SPAN><SPAN
lang=EN-US>CPU</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">要完成什么样的操作，而操作数是操作码的对象。单字节指令只有操作码，隐含操作数；双字节指令，第一个字节是操作码，第二个字节是操作数；三字节指令第一个字节是操作码，后二个字节是操作数。</SPAN><SPAN
lang=EN-US>CPU</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">在取指令的时候是先取操作码再取操作数，如何判断是操作码还是操作数就是通过取指令的顺序。而取指令的顺序完全由指令计数器</SPAN><SPAN
lang=EN-US>PC</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">来控制，因此，一旦</SPAN><SPAN
lang=EN-US>PC</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">受干扰出现错误程序便会脱离正常轨道，出现“乱飞”，这样就会使得把操作数当作操作码，或者把操作码当作操作数的情况。但只要</SPAN><SPAN
lang=EN-US>PC</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">指针落在单字节指令上程序就可纳入正轨，所以为了快速的将程序纳入正轨，我们应该多用单字节指令，并在关键的地方人为的插入一些单字节指令</SPAN><SPAN
lang=EN-US>NOP</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">，或将有效的单字节指令重写，这就称之为指令冗余。</SPAN></P>
<P class=MsoNormal style="TEXT-INDENT: 21.75pt"><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">常用的方法就是在一些双字节，三字节指令后面插入两个单字节指令</SPAN><SPAN
lang=EN-US>NOP</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">，或在一些对程序的流向起决定作用的指令前面插入两条</SPAN><SPAN
lang=EN-US>NOP</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">指令。还可对一些重要的指令进行重复放置。</SPAN></P>
<P class=MsoNormal style="TEXT-INDENT: 21.75pt"><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">但采用指令冗余技术将程序纳入正轨的条件是：乱飞的</SPAN><SPAN
lang=EN-US>PC</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">必须指向程序运行区。</SPAN></P>
<P class=MsoNormal><B><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">二、软件陷阱技术</SPAN><SPAN
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