关于定时的问题

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< class=MsoNormal style="MARGIN: 0pt"><SPAN lang=EN-US><FONT size=3>#include &lt;hidef.h&gt;<SPAN style="mso-spacerun: yes">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; </SPAN>/* common defines and macros */</FONT></SPAN></P><P class=MsoNormal style="MARGIN: 0pt"><SPAN lang=EN-US><FONT size=3>#include &lt;mc9s12dg128.h&gt;<SPAN style="mso-spacerun: yes">&nbsp;&nbsp;&nbsp;&nbsp; </SPAN>/* derivative information */</FONT></SPAN></P><P class=MsoNormal style="MARGIN: 0pt"><SPAN lang=EN-US><FONT size=3>#pragma LINK_INFO DERIVATIVE "mc9s12dg128b"</FONT></SPAN></P><P class=MsoNormal style="MARGIN: 0pt"><SPAN lang=EN-US><?xml:namespace prefix = o ns = "urn:schemas-microsoft-comffice:office" /><o:p><FONT size=3>&nbsp;</FONT></o:p></SPAN></P><P class=MsoNormal style="MARGIN: 0pt"><SPAN lang=EN-US><FONT size=3><SPAN style="mso-spacerun: yes">&nbsp;</SPAN><SPAN style="mso-spacerun: yes">&nbsp;</SPAN></FONT></SPAN></P><P class=MsoNormal style="MARGIN: 0pt"><SPAN lang=EN-US><FONT size=3>void main(void) </FONT></SPAN></P><P class=MsoNormal style="MARGIN: 0pt"><SPAN lang=EN-US><FONT size=3>{<SPAN style="mso-spacerun: yes">&nbsp; </SPAN></FONT></SPAN></P><P class=MsoNormal style="MARGIN: 0pt; TEXT-INDENT: 10.5pt; mso-char-indent-count: 1.0"><SPAN lang=EN-US><FONT size=3>DDRB=0xff; </FONT></SPAN></P><P class=MsoNormal style="MARGIN: 0pt"><SPAN lang=EN-US><FONT size=3><SPAN style="mso-spacerun: yes">&nbsp; </SPAN>PORTB=0xff; </FONT></SPAN></P><P class=MsoNormal style="MARGIN: 0pt"><SPAN lang=EN-US><FONT size=3><SPAN style="mso-spacerun: yes">&nbsp; </SPAN>TSCR2=0x05; </FONT></SPAN></P><P class=MsoNormal style="MARGIN: 0pt"><SPAN lang=EN-US><FONT size=3><SPAN style="mso-spacerun: yes">&nbsp; </SPAN>TSCR1=0x80; </FONT></SPAN></P><P class=MsoNormal style="MARGIN: 0pt"><SPAN lang=EN-US><FONT size=3><SPAN style="mso-spacerun: yes">&nbsp; </SPAN>DDRB=0xff; </FONT></SPAN></P><P class=MsoNormal style="MARGIN: 0pt"><SPAN lang=EN-US><FONT size=3><SPAN style="mso-spacerun: yes">&nbsp; </SPAN>PORTB=0xff;</FONT></SPAN></P><P class=MsoNormal style="MARGIN: 0pt"><SPAN lang=EN-US><FONT size=3><SPAN style="mso-spacerun: yes">&nbsp; </SPAN>TCNT=0x0002;</FONT></SPAN></P><P class=MsoNormal style="MARGIN: 0pt"><SPAN lang=EN-US><FONT size=3><SPAN style="mso-spacerun: yes">&nbsp; </SPAN>if (TFLG2==0x80 )</FONT></SPAN></P><P class=MsoNormal style="MARGIN: 0pt"><SPAN lang=EN-US><FONT size=3><SPAN style="mso-spacerun: yes">&nbsp;&nbsp; </SPAN>TSCR1=0x00;</FONT></SPAN></P><P class=MsoNormal style="MARGIN: 0pt"><SPAN lang=EN-US><FONT size=3><SPAN style="mso-spacerun: yes">&nbsp;&nbsp; </SPAN>PORTB=0x7E;</FONT></SPAN></P><P class=MsoNormal style="MARGIN: 0pt"><SPAN lang=EN-US><FONT size=3>}</FONT></SPAN></P><P class=MsoNormal style="MARGIN: 0pt"><SPAN lang=EN-US><FONT size=3>每次运行完定时计数寄存器的值都不同，如果在最后加上如下程序后，B口没有输出 请问这是哪的问题</FONT></SPAN></P><P class=MsoNormal style="MARGIN: 0pt"><SPAN lang=EN-US><FONT size=3>TCNT=0x0002;</P><P class=MsoNormal style="MARGIN: 0pt"><SPAN lang=EN-US><FONT size=3><SPAN style="mso-spacerun: yes">&nbsp; </SPAN>if (TFLG2==0x80 )</FONT></SPAN></P><P class=MsoNormal style="MARGIN: 0pt"><SPAN lang=EN-US><FONT size=3><SPAN style="mso-spacerun: yes">&nbsp;&nbsp; </SPAN>TSCR1=0x00;</FONT></SPAN></P><P class=MsoNormal style="MARGIN: 0pt"><SPAN lang=EN-US><FONT size=3><SPAN style="mso-spacerun: yes">&nbsp;&nbsp; </SPAN>PORTB=0xdb;</FONT></SPAN></P></FONT></SPAN>