?? 第六課 變 量 (上課所提到變量就是一種在程序執行過程中其值能不斷變......) 第六課范例程序包.htm
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<font color="#FF0000">單片機的c語言教程...由磁動力工作室明浩編寫.51單片機學習網(深圳學林電子有限公司)友情轉載</font>
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<TD class=TopLighNav1
height=22><font font> 第六課:變量</font></TD></TR></TBODY></TABLE></TH></TR></TBODY></TABLE></DIV></TD></TR></TBODY></TABLE></TD></TR>
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<DIV align=center><FONT face=黑體 font size="4">第六課 變量</FONT></DIV></TD></TR>
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<p style="line-height: 200%"><font font> 上課所提到變量就是一種在程序執行過程中其值能不斷變化的量。要在程序中使用變量必須先用標識符作為變量名,并指出所用的數據類型和存儲模式,這樣編譯系統才能為變量分配相應的存儲空間。定義一個變量的格式如下:<BR> [存儲種類] 數據類型 [存儲器類型] 變量名表<BR> 在定義格式中除了數據類型和變量名表是必要的,其它都是可選項。存儲種類有四種:自動(auto),外部(extern),靜態(static)和寄存器(register),缺省類型為自動(auto)。這些存儲種類的具體含義和用法,將在第七課《變量的存儲》中進一步進行學習。<BR> 而這里的數據類型則是和我們在第四課中學習到的名種數據類型的定義是一樣的。說明了一個變量的數據類型后,還可選擇說明該變量的存儲器類型。存儲器類型的說明就是指定該變量在C51硬件系統中所使用的存儲區域,并在編譯時準確的定位。表6-1中是KEIL
uVision2所能認別的存儲器類型。注意的是在AT89C51芯片中RAM只有低128位,位于80H到FFH的高128位則在52芯片中才有用,并和特殊寄存器地址重疊。特殊寄存器(SFR)的地址表請看附錄二 AT89C51特殊功能寄存器列表</font>
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<P align=center class=MsoNormal
style="TEXT-ALIGN: center"><SPAN
style="FONT-FAMILY: 宋體"><font font>存儲器類型<SPAN
lang=EN-US><O:P></O:P></SPAN></font></SPAN></P></TD>
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style="BORDER-BOTTOM: windowtext 0.5pt solid; BORDER-LEFT: medium none; BORDER-RIGHT: windowtext 0.5pt solid; BORDER-TOP: windowtext 0.5pt solid; PADDING-BOTTOM: 0cm; PADDING-LEFT: 5.4pt; PADDING-RIGHT: 5.4pt; PADDING-TOP: 0cm; WIDTH: 304pt; mso-border-left-alt: solid windowtext .5pt"
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<P align=center class=MsoNormal
style="TEXT-ALIGN: center"><SPAN
style="FONT-FAMILY: 宋體"><font font>說 明<SPAN
lang=EN-US><O:P></O:P></SPAN></font></SPAN></P></TD></TR>
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<P align=center class=MsoNormal
style="TEXT-ALIGN: center"><SPAN lang=EN-US
style="FONT-FAMILY: 宋體"><font font>data<O:P></O:P></font></SPAN></P></TD>
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style="BORDER-BOTTOM: windowtext 0.5pt solid; BORDER-LEFT: medium none; BORDER-RIGHT: windowtext 0.5pt solid; BORDER-TOP: medium none; PADDING-BOTTOM: 0cm; PADDING-LEFT: 5.4pt; PADDING-RIGHT: 5.4pt; PADDING-TOP: 0cm; WIDTH: 304pt; mso-border-left-alt: solid windowtext .5pt; mso-border-top-alt: solid windowtext .5pt"
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<P align=center class=MsoNormal
style="TEXT-ALIGN: center"><SPAN
style="FONT-FAMILY: 宋體"><font font>直接訪問內部數據存儲器(<SPAN
lang=EN-US>128字節),訪問速度最快<O:P></O:P></SPAN></font></SPAN></P></TD></TR>
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