?? 杭州電子&計(jì)算機(jī)工作室 歡迎您！ welcome to hangzhou electron & computer studio.htm
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<P class=MsoNormal style="TEXT-ALIGN: center"
align=center><SPAN lang=EN-US>P3.0</SPAN></P></TD>
<TD
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vAlign=top width=284>
<P class=MsoNormal style="TEXT-ALIGN: center"
align=center><SPAN
style="FONT-FAMILY: 宋體; mso-hansi-font-family: 'Times New Roman'; mso-ascii-font-family: 'Times New Roman'">串行通訊輸入（</SPAN><SPAN
lang=EN-US>RXD</SPAN><SPAN
style="FONT-FAMILY: 宋體; mso-hansi-font-family: 'Times New Roman'; mso-ascii-font-family: 'Times New Roman'">）</SPAN></P></TD></TR>
<TR>
<TD
style="BORDER-RIGHT: windowtext 0.5pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: medium none; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: windowtext 0.5pt solid; WIDTH: 213.2pt; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 0.5pt solid; mso-border-top-alt: solid windowtext .5pt"
vAlign=top width=284>
<P class=MsoNormal style="TEXT-ALIGN: center"
align=center><SPAN lang=EN-US>P3.1</SPAN></P></TD>
<TD
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vAlign=top width=284>
<P class=MsoNormal style="TEXT-ALIGN: center"
align=center><SPAN
style="FONT-FAMILY: 宋體; mso-hansi-font-family: 'Times New Roman'; mso-ascii-font-family: 'Times New Roman'">串行通訊輸出（</SPAN><SPAN
lang=EN-US>TXD</SPAN><SPAN
style="FONT-FAMILY: 宋體; mso-hansi-font-family: 'Times New Roman'; mso-ascii-font-family: 'Times New Roman'">）</SPAN></P></TD></TR>
<TR>
<TD
style="BORDER-RIGHT: windowtext 0.5pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: medium none; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: windowtext 0.5pt solid; WIDTH: 213.2pt; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 0.5pt solid; mso-border-top-alt: solid windowtext .5pt"
vAlign=top width=284>
<P class=MsoNormal style="TEXT-ALIGN: center"
align=center><SPAN lang=EN-US>P3.2</SPAN></P></TD>
<TD
style="BORDER-RIGHT: windowtext 0.5pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: medium none; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: medium none; WIDTH: 213.2pt; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 0.5pt solid; mso-border-left-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext .5pt"
vAlign=top width=284>
<P class=MsoNormal style="TEXT-ALIGN: center"
align=center><SPAN
style="FONT-FAMILY: 宋體; mso-hansi-font-family: 'Times New Roman'; mso-ascii-font-family: 'Times New Roman'">外部中斷</SPAN><SPAN
lang=EN-US>0</SPAN><SPAN
style="FONT-FAMILY: 宋體; mso-hansi-font-family: 'Times New Roman'; mso-ascii-font-family: 'Times New Roman'">（</SPAN>
<SPAN lang=EN-US>INT0</SPAN><SPAN
style="FONT-FAMILY: 宋體; mso-hansi-font-family: 'Times New Roman'; mso-ascii-font-family: 'Times New Roman'">）</SPAN></P></TD></TR>
<TR>
<TD
style="BORDER-RIGHT: windowtext 0.5pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: medium none; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: windowtext 0.5pt solid; WIDTH: 213.2pt; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 0.5pt solid; mso-border-top-alt: solid windowtext .5pt"
vAlign=top width=284>
<P class=MsoNormal style="TEXT-ALIGN: center"
align=center><SPAN lang=EN-US>P3.3</SPAN></P></TD>
<TD
style="BORDER-RIGHT: windowtext 0.5pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: medium none; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: medium none; WIDTH: 213.2pt; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 0.5pt solid; mso-border-left-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext .5pt"
vAlign=top width=284>
<P class=MsoNormal style="TEXT-ALIGN: center"
align=center><SPAN
style="FONT-FAMILY: 宋體; mso-hansi-font-family: 'Times New Roman'; mso-ascii-font-family: 'Times New Roman'">外部中斷</SPAN><SPAN
lang=EN-US>1</SPAN><SPAN
style="FONT-FAMILY: 宋體; mso-hansi-font-family: 'Times New Roman'; mso-ascii-font-family: 'Times New Roman'">（</SPAN><SPAN
lang=EN-US>INT1</SPAN><SPAN
style="FONT-FAMILY: 宋體; mso-hansi-font-family: 'Times New Roman'; mso-ascii-font-family: 'Times New Roman'">）</SPAN></P></TD></TR>
<TR>
<TD
style="BORDER-RIGHT: windowtext 0.5pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: medium none; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: windowtext 0.5pt solid; WIDTH: 213.2pt; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 0.5pt solid; mso-border-top-alt: solid windowtext .5pt"
vAlign=top width=284>
<P class=MsoNormal style="TEXT-ALIGN: center"
align=center><SPAN lang=EN-US>P3.4</SPAN></P></TD>
<TD
style="BORDER-RIGHT: windowtext 0.5pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: medium none; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: medium none; WIDTH: 213.2pt; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 0.5pt solid; mso-border-left-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext .5pt"
vAlign=top width=284>
<P class=MsoNormal style="TEXT-ALIGN: center"
align=center><SPAN
style="FONT-FAMILY: 宋體; mso-hansi-font-family: 'Times New Roman'; mso-ascii-font-family: 'Times New Roman'">定時(shí)器</SPAN><SPAN
lang=EN-US>0</SPAN><SPAN
style="FONT-FAMILY: 宋體; mso-hansi-font-family: 'Times New Roman'; mso-ascii-font-family: 'Times New Roman'">輸入</SPAN><SPAN
lang=EN-US>(T0)</SPAN></P></TD></TR>
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<TD
style="BORDER-RIGHT: windowtext 0.5pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: medium none; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: windowtext 0.5pt solid; WIDTH: 213.2pt; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 0.5pt solid; mso-border-top-alt: solid windowtext .5pt"
vAlign=top width=284 height=15>
<P class=MsoNormal style="TEXT-ALIGN: center"
align=center><SPAN lang=EN-US>P3.5</SPAN></P></TD>
<TD
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vAlign=top width=284 height=15>
<P class=MsoNormal style="TEXT-ALIGN: center"
align=center><SPAN
style="FONT-FAMILY: 宋體; mso-hansi-font-family: 'Times New Roman'; mso-ascii-font-family: 'Times New Roman'">定時(shí)器</SPAN><SPAN
lang=EN-US>1</SPAN><SPAN
style="FONT-FAMILY: 宋體; mso-hansi-font-family: 'Times New Roman'; mso-ascii-font-family: 'Times New Roman'">輸入</SPAN><SPAN
lang=EN-US>(T1)</SPAN></P></TD></TR>
<TR>
<TD
style="BORDER-RIGHT: windowtext 0.5pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: medium none; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: windowtext 0.5pt solid; WIDTH: 213.2pt; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 0.5pt solid; mso-border-top-alt: solid windowtext .5pt"
vAlign=top width=284>
<P class=MsoNormal style="TEXT-ALIGN: center"
align=center><SPAN lang=EN-US>P3.6</SPAN></P></TD>
<TD
style="BORDER-RIGHT: windowtext 0.5pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: medium none; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: medium none; WIDTH: 213.2pt; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 0.5pt solid; mso-border-left-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext .5pt"
vAlign=top width=284>
<P class=MsoNormal style="TEXT-ALIGN: center"
align=center><SPAN
style="FONT-FAMILY: 宋體; mso-hansi-font-family: 'Times New Roman'; mso-ascii-font-family: 'Times New Roman'">外部數(shù)據(jù)存儲(chǔ)器寫選通</SPAN><SPAN
lang=EN-US>WR</SPAN></P></TD></TR>
<TR>
<TD
style="BORDER-RIGHT: windowtext 0.5pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: medium none; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: windowtext 0.5pt solid; WIDTH: 213.2pt; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 0.5pt solid; mso-border-top-alt: solid windowtext .5pt"
vAlign=top width=284>
<P class=MsoNormal style="TEXT-ALIGN: center"
align=center><SPAN lang=EN-US>P3.7</SPAN></P></TD>
<TD
style="BORDER-RIGHT: windowtext 0.5pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: medium none; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: medium none; WIDTH: 213.2pt; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 0.5pt solid; mso-border-left-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext .5pt"
vAlign=top width=284>
<P class=MsoNormal style="TEXT-ALIGN: center"
align=center><SPAN
style="FONT-FAMILY: 宋體; mso-hansi-font-family: 'Times New Roman'; mso-ascii-font-family: 'Times New Roman'">外部數(shù)據(jù)存儲(chǔ)器寫選通</SPAN><SPAN
lang=EN-US>RD</SPAN></P></TD></TR></TBODY></TABLE></TD></TR>
<TR>
<TD>
<DIV align=center>表2－2 P3端口引腳兼用功能表<BR></DIV></TD></TR>
<TR>
<TD> 呼！一口氣說(shuō)了那么多，停一下吧。嗯，什么？什么叫上拉電阻？上拉電阻簡(jiǎn)單來(lái)說(shuō)就是把電平拉高，通常用4.7－10K的電阻接到Vcc電源，下拉電阻則是把電平拉低，電阻接到GND地線上。具體說(shuō)明也不是這里要討論的，接下來(lái)還是接著看其它的引腳功能吧。<BR> 5.其它的控制或復(fù)用引腳<BR> (1)
ALE/PROG 30
訪問(wèn)外部存儲(chǔ)器時(shí)，ALE（地址鎖存允許）的輸出用于鎖存地址的低位字節(jié)。即使不訪問(wèn)外部存儲(chǔ)器，ALE端仍以不變的頻率輸出脈沖信號(hào)(此頻率是振蕩器頻率的1/6)。在訪問(wèn)外部數(shù)據(jù)存儲(chǔ)器時(shí)，出現(xiàn)一個(gè)ALE脈沖。對(duì)Flash存儲(chǔ)器編程時(shí)，這個(gè)引腳用于輸入編程脈沖PROG<BR> (2)
PSEN 29
該引是外部程序存儲(chǔ)器的選通信號(hào)輸出端。當(dāng)AT89C51由外部程序存儲(chǔ)器取指令或常數(shù)時(shí)，每個(gè)機(jī)器周期輸出2個(gè)脈沖即兩次有效。但訪問(wèn)外部數(shù)據(jù)存儲(chǔ)器時(shí)，將不會(huì)有脈沖輸出。<BR> (3)
EA/Vpp 31
外部訪問(wèn)允許端。當(dāng)該引腳訪問(wèn)外部程序存儲(chǔ)器時(shí)，應(yīng)輸入低電平。要使AT89C51只訪問(wèn)外部程序存儲(chǔ)器（地址為0000H-FFFFH）,這時(shí)該引腳必須保持低電平，而要使用片內(nèi)的程序存儲(chǔ)器時(shí)該引腳必須保持高電平。對(duì)Flash存儲(chǔ)器編程時(shí)，該引腳用于施加Vpp編程電壓。Vpp電壓有兩種，類似芯片最大頻率值要根據(jù)附加的編號(hào)或芯片內(nèi)的特征字決定。具體如表2－3所列。<BR></TD></TR>
<TR>
<TD>
<TABLE
style="BORDER-RIGHT: medium none; BORDER-TOP: medium none; BORDER-LEFT: medium none; BORDER-BOTTOM: medium none; BORDER-COLLAPSE: collapse; mso-border-alt: solid windowtext .5pt; mso-padding-alt: 0cm 5.4pt 0cm 5.4pt"
cellSpacing=0 cellPadding=0 align=center border=1>
<TBODY>
<TR>
<TD
style="BORDER-RIGHT: windowtext 0.5pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: windowtext 0.5pt solid; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: windowtext 0.5pt solid; WIDTH: 142.1pt; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 0.5pt solid"
vAlign=top width=189>
<P class=MsoNormal style="TEXT-ALIGN: center"
align=center><SPAN lang=EN-US
style="FONT-FAMILY: 宋體"><O:P></O:P></SPAN></P></TD>
<TD
style="BORDER-RIGHT: windowtext 0.5pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: windowtext 0.5pt solid; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: medium none; WIDTH: 142.15pt; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 0.5pt solid; mso-border-left-alt: solid windowtext .5pt"
vAlign=top width=190 colSpan=2>
<P class=MsoNormal style="TEXT-ALIGN: center"
align=center><SPAN lang=EN-US style="FONT-FAMILY: 宋體">Vpp =
12V<O:P></O:P></SPAN></P></TD>
<TD
style="BORDER-RIGHT: windowtext 0.5pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: windowtext 0.5pt solid; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: medium none; WIDTH: 142.15pt; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 0.5pt solid; mso-border-left-alt: solid windowtext .5pt"
vAlign=top width=190 colSpan=2>
<P class=MsoNormal style="TEXT-ALIGN: center"
align=center><SPAN lang=EN-US style="FONT-FAMILY: 宋體">Vpp =
5V<O:P></O:P></SPAN></P></TD></TR>
<TR style="HEIGHT: 48.25pt">
<TD
style="BORDER-RIGHT: windowtext 0.5pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: medium none; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: windowtext 0.5pt solid; WIDTH: 142.1pt; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 0.5pt solid; HEIGHT: 48.25pt; mso-border-top-alt: solid windowtext .5pt"
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