一、基于單片機的信號發生器設計方案
信號(hao)發生器用(yong)于(yu)調節(jie)射(she)頻(pin)匹配電路，可(ke)以(yi)自(zi)行設計，一般普通的信號(hao)發生器需(xu)要輸出正弦波(bo)、方波(bo)、三角波(bo)以(yi)及(ji)鋸齒(chi)波(bo)等信號(hao)，可(ke)通過(guo)按鍵(jian)調節(jie)信號(hao)的頻(pin)率以(yi)及(ji)信號(hao)的幅度，其具體(ti)的設計方案如下：
1、總體方案設計
信(xin)(xin)(xin)號(hao)(hao)發生(sheng)器(qi)發送出(chu)(chu)去的(de)(de)(de)(de)(de)是(shi)模(mo)擬(ni)(ni)信(xin)(xin)(xin)號(hao)(hao)，而單(dan)片(pian)(pian)機(ji)輸(shu)出(chu)(chu)的(de)(de)(de)(de)(de)是(shi)數字信(xin)(xin)(xin)號(hao)(hao)，因此(ci)在設計信(xin)(xin)(xin)號(hao)(hao)發生(sheng)器(qi)系(xi)統(tong)時(shi)，需要(yao)使用到數模(mo)轉(zhuan)換芯片(pian)(pian)，可選(xuan)擇(ze)數模(mo)轉(zhuan)換芯片(pian)(pian)DAC0832，然(ran)后再(zai)利用運(yun)算放大(da)器(qi)將DAC0832輸(shu)出(chu)(chu)的(de)(de)(de)(de)(de)電(dian)(dian)流信(xin)(xin)(xin)號(hao)(hao)轉(zhuan)換成(cheng)電(dian)(dian)壓(ya)(ya)信(xin)(xin)(xin)號(hao)(hao)。這樣信(xin)(xin)(xin)號(hao)(hao)發生(sheng)器(qi)便輸(shu)出(chu)(chu)了模(mo)擬(ni)(ni)電(dian)(dian)壓(ya)(ya)。系(xi)統(tong)要(yao)輸(shu)出(chu)(chu)各種(zhong)波(bo)(bo)(bo)形信(xin)(xin)(xin)號(hao)(hao)，則要(yao)求DAC0832在運(yun)放的(de)(de)(de)(de)(de)作用下(xia)，在不(bu)(bu)(bu)同(tong)時(shi)間點輸(shu)出(chu)(chu)不(bu)(bu)(bu)同(tong)的(de)(de)(de)(de)(de)電(dian)(dian)壓(ya)(ya)值，再(zai)將這些電(dian)(dian)壓(ya)(ya)值連(lian)接起來，便構成(cheng)了相應(ying)的(de)(de)(de)(de)(de)波(bo)(bo)(bo)形信(xin)(xin)(xin)號(hao)(hao)。而要(yao)得(de)到不(bu)(bu)(bu)同(tong)的(de)(de)(de)(de)(de)電(dian)(dian)壓(ya)(ya)值，則單(dan)片(pian)(pian)機(ji)需要(yao)將8位(wei)I/O口(kou)接到DAC0832芯片(pian)(pian)的(de)(de)(de)(de)(de)8位(wei)數據信(xin)(xin)(xin)號(hao)(hao)輸(shu)入端，單(dan)片(pian)(pian)機(ji)通過(guo)改(gai)變(bian)8位(wei)I/O口(kou)的(de)(de)(de)(de)(de)數字信(xin)(xin)(xin)號(hao)(hao)，便可以(yi)在DAC0832以(yi)及運(yun)放的(de)(de)(de)(de)(de)作用下(xia)，得(de)到不(bu)(bu)(bu)同(tong)的(de)(de)(de)(de)(de)電(dian)(dian)壓(ya)(ya)值，再(zai)在時(shi)間的(de)(de)(de)(de)(de)作用下(xia)形成(cheng)不(bu)(bu)(bu)同(tong)的(de)(de)(de)(de)(de)波(bo)(bo)(bo)形信(xin)(xin)(xin)號(hao)(hao)。波(bo)(bo)(bo)形信(xin)(xin)(xin)號(hao)(hao)頻率的(de)(de)(de)(de)(de)的(de)(de)(de)(de)(de)變(bian)化(hua)可通過(guo)改(gai)變(bian)單(dan)片(pian)(pian)機(ji)8位(wei)I/O輸(shu)出(chu)(chu)口(kou)的(de)(de)(de)(de)(de)數據變(bian)化(hua)率來實現。
波(bo)形信(xin)號的(de)(de)幅(fu)度(du)由(you)DAC0832的(de)(de)參考(kao)電(dian)壓VREF來決(jue)定，為了確保VREF的(de)(de)大小可(ke)變(bian)，本系統使用到(dao)了芯片(pian)PCF8591，將PCF8591芯片(pian)的(de)(de)模擬(ni)電(dian)壓輸出端接在DAC0832的(de)(de)VREF上(shang)，通(tong)過改變(bian)PCF8591模擬(ni)電(dian)壓輸出值(zhi)便(bian)可(ke)改變(bian)VREF值(zhi)，從(cong)而改變(bian)波(bo)形信(xin)號的(de)(de)幅(fu)度(du)值(zhi)。而PCF8591的(de)(de)模擬(ni)電(dian)壓輸出值(zhi)則是尤其I2C總行(xing)上(shang)的(de)(de)數據所決(jue)定，利用單片(pian)機的(de)(de)I/O口(kou)模擬(ni)I2C與(yu)PCF8591進行(xing)通(tong)信(xin)，那么(me)單片(pian)機便(bian)可(ke)通(tong)過I/O口(kou)控(kong)制VREF電(dian)壓的(de)(de)變(bian)化，從(cong)而控(kong)制波(bo)形的(de)(de)幅(fu)度(du)變(bian)化。
2、系統硬件設計
（1）晶振電路設計
單片(pian)機(ji)(ji)穩定(ding)(ding)(ding)(ding)工作則需(xu)要穩定(ding)(ding)(ding)(ding)的(de)(de)(de)(de)(de)時(shi)(shi)(shi)鐘信(xin)號(hao)，而時(shi)(shi)(shi)鐘信(xin)號(hao)則是(shi)由晶(jing)(jing)振(zhen)電路(lu)產生，因(yin)此晶(jing)(jing)振(zhen)電路(lu)設計的(de)(de)(de)(de)(de)好(hao)壞直接(jie)(jie)影響到最小(xiao)系統(tong)的(de)(de)(de)(de)(de)穩定(ding)(ding)(ding)(ding)性。單片(pian)機(ji)(ji)的(de)(de)(de)(de)(de)18腳(jiao)(jiao)和19腳(jiao)(jiao)為晶(jing)(jing)振(zhen)連接(jie)(jie)輸入腳(jiao)(jiao)，將晶(jing)(jing)振(zhen)X1的(de)(de)(de)(de)(de)兩(liang)端連接(jie)(jie)到單片(pian)機(ji)(ji)18和19腳(jiao)(jiao)之(zhi)后(hou)便會(hui)產生時(shi)(shi)(shi)鐘信(xin)號(hao)，此時(shi)(shi)(shi)的(de)(de)(de)(de)(de)信(xin)號(hao)會(hui)存在不穩定(ding)(ding)(ding)(ding)的(de)(de)(de)(de)(de)問題，需(xu)要在晶(jing)(jing)振(zhen)Y1的(de)(de)(de)(de)(de)兩(liang)端分別外接(jie)(jie)一個22PF電容(rong)C1、C2到GND，該電容(rong)為晶(jing)(jing)振(zhen)的(de)(de)(de)(de)(de)匹(pi)(pi)配電容(rong)，晶(jing)(jing)振(zhen)匹(pi)(pi)配了電容(rong)之(zhi)后(hou)，那么產生的(de)(de)(de)(de)(de)時(shi)(shi)(shi)鐘信(xin)號(hao)就比較(jiao)穩定(ding)(ding)(ding)(ding)。出現的(de)(de)(de)(de)(de)頻偏(pian)也(ye)是(shi)在20PPM的(de)(de)(de)(de)(de)范圍內。這(zhe)樣才(cai)能確保系統(tong)時(shi)(shi)(shi)鐘穩定(ding)(ding)(ding)(ding)可靠。
（2）復位電路設計
最(zui)小系統除了(le)晶振電(dian)路之(zhi)外(wai)，還需要(yao)具(ju)備(bei)復(fu)位(wei)電(dian)路，單片機(ji)上電(dian)后，啟動的(de)時候(hou)，需要(yao)復(fu)位(wei)電(dian)路先(xian)進行(xing)(xing)復(fu)位(wei)，確保系統運行(xing)(xing)的(de)起始地址(zhi)一致(zhi) ，保證系統工作的(de)穩定性，復(fu)位(wei)是(shi)利用電(dian)容C3與R1來實(shi)現(xian)的(de)。
（3）波形幅度調節電路設計
為改(gai)變系(xi)統(tong)輸出(chu)的(de)(de)波形幅度值，本系(xi)統(tong)使用到了(le)PCF8591芯(xin)片(pian)(pian)(pian)(pian)(pian)，該(gai)芯(xin)片(pian)(pian)(pian)(pian)(pian)是一個(ge)8位CMOS數(shu)據采(cai)集(ji)器，該(gai)芯(xin)片(pian)(pian)(pian)(pian)(pian)可以將(jiang)模(mo)(mo)擬(ni)信號(hao)轉(zhuan)(zhuan)換(huan)成數(shu)字信號(hao)，再(zai)通過(guo)I2C數(shu)據總線將(jiang)該(gai)數(shu)字信號(hao)發送給單(dan)(dan)片(pian)(pian)(pian)(pian)(pian)機(ji)；也(ye)可以反過(guo)來，單(dan)(dan)片(pian)(pian)(pian)(pian)(pian)機(ji)通過(guo)I2C總線將(jiang)數(shu)字信號(hao)發送給PCF8591芯(xin)片(pian)(pian)(pian)(pian)(pian)，再(zai)由該(gai)芯(xin)片(pian)(pian)(pian)(pian)(pian)進行數(shu)模(mo)(mo)轉(zhuan)(zhuan)換(huan)后(hou)，變成模(mo)(mo)擬(ni)電(dian)壓(ya)再(zai)由AOUT腳(jiao)輸出(chu)。利用這一原理，本系(xi)統(tong)為了(le)調(diao)節(jie)信號(hao)發生器的(de)(de)幅度值，將(jiang)單(dan)(dan)片(pian)(pian)(pian)(pian)(pian)機(ji)P2.0和P2.1模(mo)(mo)擬(ni)I2C與PCF8591通信，這樣單(dan)(dan)片(pian)(pian)(pian)(pian)(pian)機(ji)便(bian)可以控制PCF8591的(de)(de)AOUT輸出(chu)端模(mo)(mo)擬(ni)電(dian)壓(ya)的(de)(de)大小，再(zai)將(jiang)其接入到DAC0832的(de)(de)VREF腳(jiao)上，便(bian)可以控制波形的(de)(de)幅度。
（4）數模轉換電路設計
信(xin)(xin)號(hao)發(fa)生(sheng)(sheng)器產生(sheng)(sheng)各(ge)種波(bo)形信(xin)(xin)號(hao)使(shi)用到了(le)DAC0832數模(mo)轉換芯(xin)(xin)片(pian)，該(gai)芯(xin)(xin)片(pian)內(nei)(nei)部集成(cheng)了(le)一(yi)(yi)個(ge)(ge)8位D/A轉換器，一(yi)(yi)個(ge)(ge)8為DAC寄存器，一(yi)(yi)個(ge)(ge)8位輸(shu)入寄存器以(yi)及(ji)一(yi)(yi)個(ge)(ge)控(kong)制電(dian)路，其內(nei)(nei)部采用的(de)(de)是倒T型R-2R電(dian)阻網絡，將該(gai)數模(mo)轉換芯(xin)(xin)片(pian)與(yu)運(yun)算放大器LM358一(yi)(yi)起(qi)使(shi)用，便可(ke)以(yi)使(shi)運(yun)放輸(shu)出端有28 =256個(ge)(ge)電(dian)壓值輸(shu)出。在不同(tong)時間內(nei)(nei)變換輸(shu)出不同(tong)的(de)(de)電(dian)壓值，使(shi)其產生(sheng)(sheng)周期性(xing)的(de)(de)變化便能形成(cheng)相(xiang)應的(de)(de)波(bo)形信(xin)(xin)號(hao)。
（5）按鍵中斷控制電路設計
基于單片(pian)(pian)機(ji)(ji)(ji)的(de)信號(hao)發生器要求輸出(chu)方(fang)波(bo)(bo)、三角(jiao)波(bo)(bo)、鋸齒(chi)波(bo)(bo)以及正弦波(bo)(bo)信號(hao)，信號(hao)的(de)幅(fu)度(du)和頻率(lv)可調，用戶可通過(guo)系(xi)統按(an)(an)(an)鍵(jian)來對信號(hao)發生器進行設(she)置。在系(xi)統中，設(she)計(ji)了8個按(an)(an)(an)鍵(jian)，其(qi)功能分別為(wei)100HZ頻率(lv)加按(an)(an)(an)鍵(jian)、1hz頻率(lv)加按(an)(an)(an)鍵(jian)、-1hz頻率(lv)減按(an)(an)(an)鍵(jian)、1V電壓幅(fu)度(du)加按(an)(an)(an)鍵(jian)、0.1V電壓幅(fu)度(du)加按(an)(an)(an)鍵(jian)、-0.1V電壓幅(fu)度(du)減按(an)(an)(an)鍵(jian)、波(bo)(bo)形切換按(an)(an)(an)鍵(jian)、掃頻開(kai)關按(an)(an)(an)鍵(jian)。為(wei)了方(fang)便系(xi)統設(she)計(ji)，采用獨立按(an)(an)(an)鍵(jian)設(she)計(ji)方(fang)法，利用單片(pian)(pian)機(ji)(ji)(ji)P1口(kou)將各按(an)(an)(an)鍵(jian)連接，通過(guo)軟(ruan)件(jian)將P1口(kou)設(she)置成上拉狀態(tai)。當沒有(you)按(an)(an)(an)鍵(jian)按(an)(an)(an)下(xia)時，單片(pian)(pian)機(ji)(ji)(ji)P1口(kou)中的(de)所有(you)I/O口(kou)檢測的(de)到(dao)時高電平；當有(you)按(an)(an)(an)鍵(jian)按(an)(an)(an)下(xia)時，則該(gai)按(an)(an)(an)鍵(jian)對應單片(pian)(pian)機(ji)(ji)(ji)的(de)I/O口(kou)會被拉低，變成低電平。單片(pian)(pian)機(ji)(ji)(ji)便能檢測到(dao)，從(cong)而調用該(gai)按(an)(an)(an)鍵(jian)程序(xu)執行相應的(de)功能。
（6）電源電路設計
本系(xi)統(tong)(tong)電(dian)(dian)(dian)(dian)路設計是(shi)在Proteus仿(fang)真軟(ruan)件上設計，該仿(fang)真軟(ruan)件有各(ge)種電(dian)(dian)(dian)(dian)源(yuan)，可直接調用(yong)。無需使用(yong)電(dian)(dian)(dian)(dian)壓轉換芯片。在本系(xi)統(tong)(tong)單片機使用(yong)5V電(dian)(dian)(dian)(dian)壓供電(dian)(dian)(dian)(dian)，而(er)(er)為(wei)了(le)使輸(shu)出波形幅度為(wei)10V，則PCF8591采用(yong)10V電(dian)(dian)(dian)(dian)壓供電(dian)(dian)(dian)(dian)，而(er)(er)運算(suan)放大器采用(yong)±15V供電(dian)(dian)(dian)(dian)，直接從仿(fang)真軟(ruan)件上取電(dian)(dian)(dian)(dian)源(yuan)即可。
3、系統軟件設計
完(wan)成(cheng)proteus軟件電路圖設(she)計(ji)之(zhi)后，接(jie)下來需(xu)要對單片機編寫(xie)驅動程(cheng)序，系統驅動程(cheng)序的編寫(xie)是在keil軟件平臺上完(wan)成(cheng)的，Keil軟件打開后，要先建立(li)工(gong)(gong)程(cheng)，然后在工(gong)(gong)程(cheng)當中(zhong)建立(li)一(yi)個.c文(wen)件，在此(ci)文(wen)件中(zhong)編寫(xie)代碼驅動程(cheng)序：
（1）系統主程序設計
主(zhu)(zhu)(zhu)程(cheng)(cheng)序(xu)(xu)是軟件(jian)系(xi)統(tong)(tong)(tong)中最為重要(yao)的(de)程(cheng)(cheng)序(xu)(xu)，因(yin)為系(xi)統(tong)(tong)(tong)程(cheng)(cheng)序(xu)(xu)是由各個(ge)子程(cheng)(cheng)序(xu)(xu)所構成，而子程(cheng)(cheng)序(xu)(xu)的(de)調用全部(bu)是在(zai)主(zhu)(zhu)(zhu)程(cheng)(cheng)序(xu)(xu)中來實現的(de)，主(zhu)(zhu)(zhu)程(cheng)(cheng)序(xu)(xu)設計的(de)好壞(huai)直(zhi)接能影響到(dao)系(xi)統(tong)(tong)(tong)的(de)邏輯結構，影響到(dao)系(xi)統(tong)(tong)(tong)工作(zuo)的(de)穩定(ding)性。在(zai)本(ben)系(xi)統(tong)(tong)(tong)中，系(xi)統(tong)(tong)(tong)開始運行(xing)后，先會(hui)執行(xing)主(zhu)(zhu)(zhu)程(cheng)(cheng)序(xu)(xu)，在(zai)主(zhu)(zhu)(zhu)程(cheng)(cheng)序(xu)(xu)中對單片(pian)機及其外圍元件(jian)進(jin)行(xing)初始化(hua)設置，完成初始化(hua)設置之后，系(xi)統(tong)(tong)(tong)就(jiu)會(hui)執行(xing)正(zheng)弦波程(cheng)(cheng)序(xu)(xu)，讓信(xin)號發(fa)(fa)生器(qi)(qi)輸(shu)出(chu)正(zheng)弦波信(xin)號，然(ran)(ran)后再去(qu)檢測是否(fou)有按(an)(an)鍵按(an)(an)下(xia)，如果(guo)有按(an)(an)鍵按(an)(an)下(xia)，系(xi)統(tong)(tong)(tong)檢測到(dao)后，便會(hui)執行(xing)相應(ying)按(an)(an)鍵的(de)程(cheng)(cheng)序(xu)(xu)，從而改(gai)變信(xin)號發(fa)(fa)生器(qi)(qi)輸(shu)出(chu)的(de)波形。如果(guo)沒有按(an)(an)鍵產生，則系(xi)統(tong)(tong)(tong)繼續保持當前波形輸(shu)出(chu)，然(ran)(ran)后再繼續去(qu)訪問是否(fou)有按(an)(an)鍵按(an)(an)下(xia)，如此(ci)循(xun)環下(xia)去(qu)。
（2）按鍵掃描程序設計
本系統(tong)是(shi)通過按(an)(an)(an)(an)(an)(an)(an)鍵(jian)(jian)(jian)(jian)(jian)來改變信號(hao)發生器的波(bo)(bo)形，系統(tong)一共有八個按(an)(an)(an)(an)(an)(an)(an)鍵(jian)(jian)(jian)(jian)(jian)，按(an)(an)(an)(an)(an)(an)(an)下不同(tong)按(an)(an)(an)(an)(an)(an)(an)鍵(jian)(jian)(jian)(jian)(jian)時，系統(tong)需要輸(shu)(shu)出(chu)不同(tong)的波(bo)(bo)形。定義(yi)按(an)(an)(an)(an)(an)(an)(an)鍵(jian)(jian)(jian)(jian)(jian)6為(wei)(wei)波(bo)(bo)形切換(huan)按(an)(an)(an)(an)(an)(an)(an)鍵(jian)(jian)(jian)(jian)(jian)，按(an)(an)(an)(an)(an)(an)(an)鍵(jian)(jian)(jian)(jian)(jian)0為(wei)(wei)100HZ頻(pin)率(lv)(lv)(lv)增(zeng)(zeng)加(jia)按(an)(an)(an)(an)(an)(an)(an)鍵(jian)(jian)(jian)(jian)(jian)，按(an)(an)(an)(an)(an)(an)(an)鍵(jian)(jian)(jian)(jian)(jian)1為(wei)(wei)1HZ頻(pin)率(lv)(lv)(lv)增(zeng)(zeng)加(jia)按(an)(an)(an)(an)(an)(an)(an)鍵(jian)(jian)(jian)(jian)(jian)，按(an)(an)(an)(an)(an)(an)(an)鍵(jian)(jian)(jian)(jian)(jian)2為(wei)(wei)1HZ頻(pin)率(lv)(lv)(lv)減按(an)(an)(an)(an)(an)(an)(an)鍵(jian)(jian)(jian)(jian)(jian)，按(an)(an)(an)(an)(an)(an)(an)鍵(jian)(jian)(jian)(jian)(jian)3位1V幅度(du)增(zeng)(zeng)加(jia)按(an)(an)(an)(an)(an)(an)(an)鍵(jian)(jian)(jian)(jian)(jian)，按(an)(an)(an)(an)(an)(an)(an)鍵(jian)(jian)(jian)(jian)(jian)4為(wei)(wei)0.1V幅度(du)增(zeng)(zeng)加(jia)按(an)(an)(an)(an)(an)(an)(an)鍵(jian)(jian)(jian)(jian)(jian)，按(an)(an)(an)(an)(an)(an)(an)鍵(jian)(jian)(jian)(jian)(jian)5為(wei)(wei)0.1V幅度(du)減小按(an)(an)(an)(an)(an)(an)(an)鍵(jian)(jian)(jian)(jian)(jian)，按(an)(an)(an)(an)(an)(an)(an)鍵(jian)(jian)(jian)(jian)(jian)7位掃頻(pin)按(an)(an)(an)(an)(an)(an)(an)鍵(jian)(jian)(jian)(jian)(jian)，flang為(wei)(wei)標志位，用于判斷按(an)(an)(an)(an)(an)(an)(an)鍵(jian)(jian)(jian)(jian)(jian)6按(an)(an)(an)(an)(an)(an)(an)下的次(ci)數當(dang)flang為(wei)(wei)1是(shi)默認輸(shu)(shu)出(chu)正弦波(bo)(bo)；當(dang)flang為(wei)(wei)2時，輸(shu)(shu)出(chu)三角波(bo)(bo)；當(dang)flang為(wei)(wei)3時輸(shu)(shu)出(chu)鋸(ju)齒波(bo)(bo)；當(dang)flang為(wei)(wei)4時，輸(shu)(shu)出(chu)方波(bo)(bo)；當(dang)flang為(wei)(wei)5時，則會令flang=1，輸(shu)(shu)出(chu)正弦波(bo)(bo)。
因(yin)此，當(dang)有按(an)(an)(an)(an)(an)鍵(jian)(jian)按(an)(an)(an)(an)(an)下時，系(xi)統(tong)調用按(an)(an)(an)(an)(an)鍵(jian)(jian)程序會去判(pan)斷(duan)是哪個(ge)按(an)(an)(an)(an)(an)鍵(jian)(jian)按(an)(an)(an)(an)(an)下，如果是按(an)(an)(an)(an)(an)鍵(jian)(jian)6按(an)(an)(an)(an)(an)下，表示需要切換信(xin)(xin)號(hao)發生器的輸(shu)出波(bo)(bo)形(xing)，令flang+1，然(ran)后判(pan)斷(duan)flang的值，再輸(shu)出相應的波(bo)(bo)形(xing)信(xin)(xin)號(hao)。當(dang)是0按(an)(an)(an)(an)(an)鍵(jian)(jian)按(an)(an)(an)(an)(an)下時，則系(xi)統(tong)會在(zai)原有的波(bo)(bo)形(xing)上，改變其輸(shu)出頻(pin)(pin)率(lv)，使(shi)頻(pin)(pin)率(lv)增加100HZ；當(dang)按(an)(an)(an)(an)(an)下的是1按(an)(an)(an)(an)(an)鍵(jian)(jian)，則將頻(pin)(pin)率(lv)增加1HZ；當(dang)2按(an)(an)(an)(an)(an)鍵(jian)(jian)按(an)(an)(an)(an)(an)下，則將頻(pin)(pin)率(lv)減(jian)小1HZ；當(dang)按(an)(an)(an)(an)(an)鍵(jian)(jian)3按(an)(an)(an)(an)(an)下時，表示要在(zai)原有波(bo)(bo)形(xing)的基礎上增加1V的波(bo)(bo)形(xing)幅(fu)度；當(dang)4按(an)(an)(an)(an)(an)鍵(jian)(jian)按(an)(an)(an)(an)(an)下，則幅(fu)度增加0.1V；當(dang)5按(an)(an)(an)(an)(an)鍵(jian)(jian)按(an)(an)(an)(an)(an)下，則幅(fu)度減(jian)小0.1V；當(dang)7按(an)(an)(an)(an)(an)鍵(jian)(jian)按(an)(an)(an)(an)(an)下，則進行掃頻(pin)(pin)。當(dang)執行完(wan)按(an)(an)(an)(an)(an)鍵(jian)(jian)程序后，返回系(xi)統(tong)主程序。
二、信號發生器的設計要求有哪些
基于單片機設計的信號發生器屬于簡易信號發生器，主要能產生方波、三角波和正弦波并進行仿真，這類信號發生器設(she)計好(hao)后，應(ying)滿足以下(xia)要求：
1、基本性能指標要求
（1）頻(pin)率范圍(wei)：100Hz~1kHz。
（2）輸出電壓：方波(bo) Up-p≤24V，三角波(bo) Up-p=6V，正弦波(bo) Up-p>1V。
2、擴展性能指標要求
頻率(lv)范圍分(fen)段(duan)設置10Hz~100Hz，100Hz~1kHz，1kHz~10kHz；波形特性方(fang)波t r<30us（1kHz，最(zui)大(da)輸出時），三角波r△<2%，正弦波r～<5%。
