一、基于單片機的信號發生器設計方案
信(xin)號(hao)(hao)(hao)(hao)發(fa)生器用于調節射頻匹(pi)配電路，可以自行設計，一般普通(tong)的(de)信(xin)號(hao)(hao)(hao)(hao)發(fa)生器需要(yao)輸出正弦(xian)波(bo)、方(fang)波(bo)、三角波(bo)以及鋸齒波(bo)等(deng)信(xin)號(hao)(hao)(hao)(hao)，可通(tong)過按鍵調節信(xin)號(hao)(hao)(hao)(hao)的(de)頻率(lv)以及信(xin)號(hao)(hao)(hao)(hao)的(de)幅度，其具體的(de)設計方(fang)案如下：
1、總體方案設計
信號(hao)(hao)(hao)(hao)發(fa)生器(qi)發(fa)送(song)出(chu)去的(de)(de)是模(mo)擬(ni)信號(hao)(hao)(hao)(hao)，而單(dan)(dan)片(pian)(pian)機(ji)(ji)輸出(chu)的(de)(de)是數字(zi)信號(hao)(hao)(hao)(hao)，因此在(zai)設計信號(hao)(hao)(hao)(hao)發(fa)生器(qi)系統時(shi)，需(xu)要使(shi)用到(dao)數模(mo)轉(zhuan)換(huan)芯片(pian)(pian)，可(ke)選擇數模(mo)轉(zhuan)換(huan)芯片(pian)(pian)DAC0832，然(ran)后再利用運算放大器(qi)將(jiang)DAC0832輸出(chu)的(de)(de)電(dian)(dian)(dian)流(liu)信號(hao)(hao)(hao)(hao)轉(zhuan)換(huan)成電(dian)(dian)(dian)壓(ya)(ya)信號(hao)(hao)(hao)(hao)。這樣(yang)信號(hao)(hao)(hao)(hao)發(fa)生器(qi)便(bian)輸出(chu)了(le)模(mo)擬(ni)電(dian)(dian)(dian)壓(ya)(ya)。系統要輸出(chu)各種波(bo)形(xing)信號(hao)(hao)(hao)(hao)，則要求DAC0832在(zai)運放的(de)(de)作用下(xia)，在(zai)不(bu)同(tong)時(shi)間點輸出(chu)不(bu)同(tong)的(de)(de)電(dian)(dian)(dian)壓(ya)(ya)值，再將(jiang)這些電(dian)(dian)(dian)壓(ya)(ya)值連(lian)接起(qi)來，便(bian)構(gou)成了(le)相應的(de)(de)波(bo)形(xing)信號(hao)(hao)(hao)(hao)。而要得到(dao)不(bu)同(tong)的(de)(de)電(dian)(dian)(dian)壓(ya)(ya)值，則單(dan)(dan)片(pian)(pian)機(ji)(ji)需(xu)要將(jiang)8位(wei)I/O口(kou)(kou)接到(dao)DAC0832芯片(pian)(pian)的(de)(de)8位(wei)數據信號(hao)(hao)(hao)(hao)輸入端，單(dan)(dan)片(pian)(pian)機(ji)(ji)通過(guo)改變8位(wei)I/O口(kou)(kou)的(de)(de)數字(zi)信號(hao)(hao)(hao)(hao)，便(bian)可(ke)以在(zai)DAC0832以及運放的(de)(de)作用下(xia)，得到(dao)不(bu)同(tong)的(de)(de)電(dian)(dian)(dian)壓(ya)(ya)值，再在(zai)時(shi)間的(de)(de)作用下(xia)形(xing)成不(bu)同(tong)的(de)(de)波(bo)形(xing)信號(hao)(hao)(hao)(hao)。波(bo)形(xing)信號(hao)(hao)(hao)(hao)頻率的(de)(de)的(de)(de)變化可(ke)通過(guo)改變單(dan)(dan)片(pian)(pian)機(ji)(ji)8位(wei)I/O輸出(chu)口(kou)(kou)的(de)(de)數據變化率來實現。
波形(xing)信號(hao)的(de)(de)幅度由DAC0832的(de)(de)參考電(dian)(dian)壓(ya)VREF來(lai)決(jue)定，為了確(que)保(bao)VREF的(de)(de)大小可(ke)(ke)變(bian)，本系統使(shi)用到(dao)了芯片PCF8591，將PCF8591芯片的(de)(de)模擬電(dian)(dian)壓(ya)輸(shu)出端接在(zai)DAC0832的(de)(de)VREF上(shang)(shang)，通(tong)過改變(bian)PCF8591模擬電(dian)(dian)壓(ya)輸(shu)出值便可(ke)(ke)改變(bian)VREF值，從而(er)改變(bian)波形(xing)信號(hao)的(de)(de)幅度值。而(er)PCF8591的(de)(de)模擬電(dian)(dian)壓(ya)輸(shu)出值則是尤(you)其I2C總行上(shang)(shang)的(de)(de)數據所決(jue)定，利用單(dan)(dan)片機(ji)的(de)(de)I/O口模擬I2C與PCF8591進行通(tong)信，那么單(dan)(dan)片機(ji)便可(ke)(ke)通(tong)過I/O口控(kong)制VREF電(dian)(dian)壓(ya)的(de)(de)變(bian)化，從而(er)控(kong)制波形(xing)的(de)(de)幅度變(bian)化。
2、系統硬件設計
（1）晶振電路設計
單片機(ji)穩定工(gong)作則需要穩定的(de)(de)(de)時(shi)(shi)鐘(zhong)(zhong)信(xin)號，而時(shi)(shi)鐘(zhong)(zhong)信(xin)號則是(shi)由晶(jing)振(zhen)電路(lu)(lu)產生，因此(ci)晶(jing)振(zhen)電路(lu)(lu)設計的(de)(de)(de)好壞(huai)直接(jie)影響到(dao)最小系統的(de)(de)(de)穩定性(xing)。單片機(ji)的(de)(de)(de)18腳(jiao)(jiao)和(he)(he)19腳(jiao)(jiao)為晶(jing)振(zhen)連接(jie)輸(shu)入腳(jiao)(jiao)，將晶(jing)振(zhen)X1的(de)(de)(de)兩(liang)端連接(jie)到(dao)單片機(ji)18和(he)(he)19腳(jiao)(jiao)之后便(bian)會產生時(shi)(shi)鐘(zhong)(zhong)信(xin)號，此(ci)時(shi)(shi)的(de)(de)(de)信(xin)號會存在不穩定的(de)(de)(de)問題，需要在晶(jing)振(zhen)Y1的(de)(de)(de)兩(liang)端分(fen)別外接(jie)一個(ge)22PF電容C1、C2到(dao)GND，該電容為晶(jing)振(zhen)的(de)(de)(de)匹(pi)配(pei)電容，晶(jing)振(zhen)匹(pi)配(pei)了(le)電容之后，那么產生的(de)(de)(de)時(shi)(shi)鐘(zhong)(zhong)信(xin)號就(jiu)比(bi)較穩定。出現的(de)(de)(de)頻偏也是(shi)在20PPM的(de)(de)(de)范圍內。這樣才能確保系統時(shi)(shi)鐘(zhong)(zhong)穩定可靠。
（2）復位電路設計
最小系統(tong)除(chu)了(le)晶振電(dian)路之外，還(huan)需要具備(bei)復位(wei)電(dian)路，單片機(ji)上電(dian)后，啟動的(de)時候，需要復位(wei)電(dian)路先(xian)進行復位(wei)，確保系統(tong)運(yun)行的(de)起始地址(zhi)一(yi)致(zhi) ，保證系統(tong)工作的(de)穩定(ding)性，復位(wei)是利用電(dian)容C3與R1來實(shi)現的(de)。
（3）波形幅度調節電路設計
為(wei)改變系(xi)統輸(shu)出的波(bo)形(xing)幅度(du)(du)值，本系(xi)統使用(yong)到了PCF8591芯(xin)片(pian)(pian)(pian)(pian)(pian)，該芯(xin)片(pian)(pian)(pian)(pian)(pian)是一個8位(wei)CMOS數據(ju)采集(ji)器，該芯(xin)片(pian)(pian)(pian)(pian)(pian)可(ke)以(yi)將模(mo)擬信號(hao)(hao)轉換(huan)成數字信號(hao)(hao)，再(zai)通(tong)過(guo)I2C數據(ju)總線將該數字信號(hao)(hao)發(fa)(fa)送給單片(pian)(pian)(pian)(pian)(pian)機(ji)(ji)(ji)；也可(ke)以(yi)反過(guo)來(lai)，單片(pian)(pian)(pian)(pian)(pian)機(ji)(ji)(ji)通(tong)過(guo)I2C總線將數字信號(hao)(hao)發(fa)(fa)送給PCF8591芯(xin)片(pian)(pian)(pian)(pian)(pian)，再(zai)由該芯(xin)片(pian)(pian)(pian)(pian)(pian)進(jin)行數模(mo)轉換(huan)后，變成模(mo)擬電(dian)壓再(zai)由AOUT腳輸(shu)出。利用(yong)這一原理，本系(xi)統為(wei)了調節信號(hao)(hao)發(fa)(fa)生器的幅度(du)(du)值，將單片(pian)(pian)(pian)(pian)(pian)機(ji)(ji)(ji)P2.0和P2.1模(mo)擬I2C與PCF8591通(tong)信，這樣單片(pian)(pian)(pian)(pian)(pian)機(ji)(ji)(ji)便可(ke)以(yi)控(kong)制(zhi)PCF8591的AOUT輸(shu)出端模(mo)擬電(dian)壓的大小，再(zai)將其接入(ru)到DAC0832的VREF腳上，便可(ke)以(yi)控(kong)制(zhi)波(bo)形(xing)的幅度(du)(du)。
（4）數模轉換電路設計
信號發生(sheng)器產(chan)生(sheng)各種波(bo)形(xing)信號使(shi)用到了DAC0832數(shu)模轉(zhuan)(zhuan)換芯(xin)片(pian)(pian)，該芯(xin)片(pian)(pian)內(nei)(nei)部集成(cheng)了一個8位D/A轉(zhuan)(zhuan)換器，一個8為DAC寄存(cun)器，一個8位輸(shu)入寄存(cun)器以及一個控制電(dian)路，其(qi)內(nei)(nei)部采用的是倒(dao)T型R-2R電(dian)阻網(wang)絡，將該數(shu)模轉(zhuan)(zhuan)換芯(xin)片(pian)(pian)與運(yun)算放(fang)大器LM358一起使(shi)用，便可以使(shi)運(yun)放(fang)輸(shu)出端有28 =256個電(dian)壓(ya)值輸(shu)出。在不同時間(jian)內(nei)(nei)變(bian)換輸(shu)出不同的電(dian)壓(ya)值，使(shi)其(qi)產(chan)生(sheng)周期性的變(bian)化便能(neng)形(xing)成(cheng)相應的波(bo)形(xing)信號。
（5）按鍵中斷控制電路設計
基(ji)于單(dan)片(pian)機(ji)(ji)的(de)信(xin)號(hao)發生器要求輸出方波、三角波、鋸齒波以及正弦(xian)波信(xin)號(hao)，信(xin)號(hao)的(de)幅(fu)度(du)(du)和頻(pin)(pin)率(lv)(lv)可調，用戶可通過系(xi)統(tong)按(an)鍵(jian)(jian)(jian)(jian)來對信(xin)號(hao)發生器進行設(she)置。在系(xi)統(tong)中，設(she)計了8個(ge)按(an)鍵(jian)(jian)(jian)(jian)，其(qi)功能(neng)分別為100HZ頻(pin)(pin)率(lv)(lv)加(jia)按(an)鍵(jian)(jian)(jian)(jian)、1hz頻(pin)(pin)率(lv)(lv)加(jia)按(an)鍵(jian)(jian)(jian)(jian)、-1hz頻(pin)(pin)率(lv)(lv)減按(an)鍵(jian)(jian)(jian)(jian)、1V電壓(ya)幅(fu)度(du)(du)加(jia)按(an)鍵(jian)(jian)(jian)(jian)、0.1V電壓(ya)幅(fu)度(du)(du)加(jia)按(an)鍵(jian)(jian)(jian)(jian)、-0.1V電壓(ya)幅(fu)度(du)(du)減按(an)鍵(jian)(jian)(jian)(jian)、波形(xing)切換按(an)鍵(jian)(jian)(jian)(jian)、掃頻(pin)(pin)開關按(an)鍵(jian)(jian)(jian)(jian)。為了方便(bian)系(xi)統(tong)設(she)計，采用獨立按(an)鍵(jian)(jian)(jian)(jian)設(she)計方法，利(li)用單(dan)片(pian)機(ji)(ji)P1口(kou)將(jiang)各按(an)鍵(jian)(jian)(jian)(jian)連接，通過軟件將(jiang)P1口(kou)設(she)置成上拉狀態。當(dang)沒有(you)按(an)鍵(jian)(jian)(jian)(jian)按(an)下時(shi)，單(dan)片(pian)機(ji)(ji)P1口(kou)中的(de)所有(you)I/O口(kou)檢(jian)測(ce)的(de)到時(shi)高電平；當(dang)有(you)按(an)鍵(jian)(jian)(jian)(jian)按(an)下時(shi)，則該按(an)鍵(jian)(jian)(jian)(jian)對應(ying)單(dan)片(pian)機(ji)(ji)的(de)I/O口(kou)會被(bei)拉低，變成低電平。單(dan)片(pian)機(ji)(ji)便(bian)能(neng)檢(jian)測(ce)到，從而調用該按(an)鍵(jian)(jian)(jian)(jian)程序執行相應(ying)的(de)功能(neng)。
（6）電源電路設計
本系(xi)統電(dian)(dian)路設計是在(zai)Proteus仿(fang)真軟件上設計，該(gai)仿(fang)真軟件有(you)各種電(dian)(dian)源，可(ke)直(zhi)接調用(yong)(yong)。無(wu)需使用(yong)(yong)電(dian)(dian)壓轉換(huan)芯片。在(zai)本系(xi)統單片機使用(yong)(yong)5V電(dian)(dian)壓供(gong)電(dian)(dian)，而為了使輸出波形幅度為10V，則PCF8591采用(yong)(yong)10V電(dian)(dian)壓供(gong)電(dian)(dian)，而運算放大器采用(yong)(yong)±15V供(gong)電(dian)(dian)，直(zhi)接從仿(fang)真軟件上取電(dian)(dian)源即可(ke)。
3、系統軟件設計
完成proteus軟件(jian)電(dian)路圖設計之(zhi)后(hou)，接下來需要對單片機編(bian)寫(xie)驅動(dong)程(cheng)(cheng)(cheng)序(xu)(xu)，系統(tong)驅動(dong)程(cheng)(cheng)(cheng)序(xu)(xu)的編(bian)寫(xie)是在(zai)keil軟件(jian)平臺上完成的，Keil軟件(jian)打開后(hou)，要先建立工程(cheng)(cheng)(cheng)，然后(hou)在(zai)工程(cheng)(cheng)(cheng)當中(zhong)建立一個(ge).c文(wen)件(jian)，在(zai)此文(wen)件(jian)中(zhong)編(bian)寫(xie)代(dai)碼(ma)驅動(dong)程(cheng)(cheng)(cheng)序(xu)(xu)：
（1）系統主程序設計
主(zhu)(zhu)程(cheng)序(xu)是軟件系統(tong)中最為重要的程(cheng)序(xu)，因為系統(tong)程(cheng)序(xu)是由各個子程(cheng)序(xu)所構成，而子程(cheng)序(xu)的調用全部(bu)是在(zai)(zai)主(zhu)(zhu)程(cheng)序(xu)中來(lai)實現的，主(zhu)(zhu)程(cheng)序(xu)設計的好壞(huai)直接能影響到(dao)(dao)系統(tong)的邏輯結構，影響到(dao)(dao)系統(tong)工作的穩定性(xing)。在(zai)(zai)本系統(tong)中，系統(tong)開始(shi)運行后(hou)，先會執行主(zhu)(zhu)程(cheng)序(xu)，在(zai)(zai)主(zhu)(zhu)程(cheng)序(xu)中對單片機及其外圍元件進行初始(shi)化(hua)設置(zhi)，完(wan)成初始(shi)化(hua)設置(zhi)之后(hou)，系統(tong)就會執行正(zheng)弦波程(cheng)序(xu)，讓信(xin)號發生(sheng)器(qi)輸(shu)(shu)出(chu)正(zheng)弦波信(xin)號，然后(hou)再(zai)去(qu)(qu)檢(jian)測是否有(you)(you)按(an)鍵(jian)(jian)按(an)下，如果有(you)(you)按(an)鍵(jian)(jian)按(an)下，系統(tong)檢(jian)測到(dao)(dao)后(hou)，便(bian)會執行相應按(an)鍵(jian)(jian)的程(cheng)序(xu)，從而改(gai)變信(xin)號發生(sheng)器(qi)輸(shu)(shu)出(chu)的波形。如果沒有(you)(you)按(an)鍵(jian)(jian)產生(sheng)，則系統(tong)繼(ji)續保(bao)持當前波形輸(shu)(shu)出(chu)，然后(hou)再(zai)繼(ji)續去(qu)(qu)訪問是否有(you)(you)按(an)鍵(jian)(jian)按(an)下，如此循環(huan)下去(qu)(qu)。
（2）按鍵掃描程序設計
本系統(tong)是通過按(an)(an)(an)(an)(an)(an)(an)(an)(an)鍵(jian)(jian)(jian)(jian)(jian)(jian)(jian)(jian)來改(gai)變信號發生器的波(bo)(bo)(bo)形，系統(tong)一共(gong)有八個按(an)(an)(an)(an)(an)(an)(an)(an)(an)鍵(jian)(jian)(jian)(jian)(jian)(jian)(jian)(jian)，按(an)(an)(an)(an)(an)(an)(an)(an)(an)下不(bu)同按(an)(an)(an)(an)(an)(an)(an)(an)(an)鍵(jian)(jian)(jian)(jian)(jian)(jian)(jian)(jian)時(shi)，系統(tong)需(xu)要輸出(chu)(chu)(chu)不(bu)同的波(bo)(bo)(bo)形。定義按(an)(an)(an)(an)(an)(an)(an)(an)(an)鍵(jian)(jian)(jian)(jian)(jian)(jian)(jian)(jian)6為(wei)波(bo)(bo)(bo)形切換按(an)(an)(an)(an)(an)(an)(an)(an)(an)鍵(jian)(jian)(jian)(jian)(jian)(jian)(jian)(jian)，按(an)(an)(an)(an)(an)(an)(an)(an)(an)鍵(jian)(jian)(jian)(jian)(jian)(jian)(jian)(jian)0為(wei)100HZ頻率(lv)增(zeng)(zeng)加按(an)(an)(an)(an)(an)(an)(an)(an)(an)鍵(jian)(jian)(jian)(jian)(jian)(jian)(jian)(jian)，按(an)(an)(an)(an)(an)(an)(an)(an)(an)鍵(jian)(jian)(jian)(jian)(jian)(jian)(jian)(jian)1為(wei)1HZ頻率(lv)增(zeng)(zeng)加按(an)(an)(an)(an)(an)(an)(an)(an)(an)鍵(jian)(jian)(jian)(jian)(jian)(jian)(jian)(jian)，按(an)(an)(an)(an)(an)(an)(an)(an)(an)鍵(jian)(jian)(jian)(jian)(jian)(jian)(jian)(jian)2為(wei)1HZ頻率(lv)減按(an)(an)(an)(an)(an)(an)(an)(an)(an)鍵(jian)(jian)(jian)(jian)(jian)(jian)(jian)(jian)，按(an)(an)(an)(an)(an)(an)(an)(an)(an)鍵(jian)(jian)(jian)(jian)(jian)(jian)(jian)(jian)3位(wei)1V幅(fu)(fu)度增(zeng)(zeng)加按(an)(an)(an)(an)(an)(an)(an)(an)(an)鍵(jian)(jian)(jian)(jian)(jian)(jian)(jian)(jian)，按(an)(an)(an)(an)(an)(an)(an)(an)(an)鍵(jian)(jian)(jian)(jian)(jian)(jian)(jian)(jian)4為(wei)0.1V幅(fu)(fu)度增(zeng)(zeng)加按(an)(an)(an)(an)(an)(an)(an)(an)(an)鍵(jian)(jian)(jian)(jian)(jian)(jian)(jian)(jian)，按(an)(an)(an)(an)(an)(an)(an)(an)(an)鍵(jian)(jian)(jian)(jian)(jian)(jian)(jian)(jian)5為(wei)0.1V幅(fu)(fu)度減小按(an)(an)(an)(an)(an)(an)(an)(an)(an)鍵(jian)(jian)(jian)(jian)(jian)(jian)(jian)(jian)，按(an)(an)(an)(an)(an)(an)(an)(an)(an)鍵(jian)(jian)(jian)(jian)(jian)(jian)(jian)(jian)7位(wei)掃頻按(an)(an)(an)(an)(an)(an)(an)(an)(an)鍵(jian)(jian)(jian)(jian)(jian)(jian)(jian)(jian)，flang為(wei)標(biao)志位(wei)，用于判斷按(an)(an)(an)(an)(an)(an)(an)(an)(an)鍵(jian)(jian)(jian)(jian)(jian)(jian)(jian)(jian)6按(an)(an)(an)(an)(an)(an)(an)(an)(an)下的次(ci)數當(dang)flang為(wei)1是默認輸出(chu)(chu)(chu)正弦(xian)波(bo)(bo)(bo)；當(dang)flang為(wei)2時(shi)，輸出(chu)(chu)(chu)三角(jiao)波(bo)(bo)(bo)；當(dang)flang為(wei)3時(shi)輸出(chu)(chu)(chu)鋸齒波(bo)(bo)(bo)；當(dang)flang為(wei)4時(shi)，輸出(chu)(chu)(chu)方波(bo)(bo)(bo)；當(dang)flang為(wei)5時(shi)，則會令flang=1，輸出(chu)(chu)(chu)正弦(xian)波(bo)(bo)(bo)。
因此，當有(you)按(an)(an)(an)(an)(an)鍵(jian)(jian)(jian)按(an)(an)(an)(an)(an)下(xia)(xia)(xia)(xia)(xia)時(shi)，系統調用按(an)(an)(an)(an)(an)鍵(jian)(jian)(jian)程(cheng)(cheng)序(xu)(xu)會去判斷(duan)是(shi)哪(na)個按(an)(an)(an)(an)(an)鍵(jian)(jian)(jian)按(an)(an)(an)(an)(an)下(xia)(xia)(xia)(xia)(xia)，如果是(shi)按(an)(an)(an)(an)(an)鍵(jian)(jian)(jian)6按(an)(an)(an)(an)(an)下(xia)(xia)(xia)(xia)(xia)，表(biao)示需要切換信(xin)號(hao)發生器(qi)的(de)(de)(de)輸(shu)出(chu)波(bo)(bo)(bo)形，令flang+1，然(ran)后判斷(duan)flang的(de)(de)(de)值，再輸(shu)出(chu)相應的(de)(de)(de)波(bo)(bo)(bo)形信(xin)號(hao)。當是(shi)0按(an)(an)(an)(an)(an)鍵(jian)(jian)(jian)按(an)(an)(an)(an)(an)下(xia)(xia)(xia)(xia)(xia)時(shi)，則(ze)系統會在原有(you)的(de)(de)(de)波(bo)(bo)(bo)形上，改變其(qi)輸(shu)出(chu)頻率(lv)，使頻率(lv)增(zeng)加(jia)100HZ；當按(an)(an)(an)(an)(an)下(xia)(xia)(xia)(xia)(xia)的(de)(de)(de)是(shi)1按(an)(an)(an)(an)(an)鍵(jian)(jian)(jian)，則(ze)將頻率(lv)增(zeng)加(jia)1HZ；當2按(an)(an)(an)(an)(an)鍵(jian)(jian)(jian)按(an)(an)(an)(an)(an)下(xia)(xia)(xia)(xia)(xia)，則(ze)將頻率(lv)減小(xiao)1HZ；當按(an)(an)(an)(an)(an)鍵(jian)(jian)(jian)3按(an)(an)(an)(an)(an)下(xia)(xia)(xia)(xia)(xia)時(shi)，表(biao)示要在原有(you)波(bo)(bo)(bo)形的(de)(de)(de)基礎(chu)上增(zeng)加(jia)1V的(de)(de)(de)波(bo)(bo)(bo)形幅度；當4按(an)(an)(an)(an)(an)鍵(jian)(jian)(jian)按(an)(an)(an)(an)(an)下(xia)(xia)(xia)(xia)(xia)，則(ze)幅度增(zeng)加(jia)0.1V；當5按(an)(an)(an)(an)(an)鍵(jian)(jian)(jian)按(an)(an)(an)(an)(an)下(xia)(xia)(xia)(xia)(xia)，則(ze)幅度減小(xiao)0.1V；當7按(an)(an)(an)(an)(an)鍵(jian)(jian)(jian)按(an)(an)(an)(an)(an)下(xia)(xia)(xia)(xia)(xia)，則(ze)進(jin)行掃頻。當執(zhi)行完按(an)(an)(an)(an)(an)鍵(jian)(jian)(jian)程(cheng)(cheng)序(xu)(xu)后，返回系統主程(cheng)(cheng)序(xu)(xu)。
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，這類信號發生器設計(ji)好后(hou)，應滿(man)足(zu)以下要(yao)求：
1、基本性能指標要求
（1）頻率范圍：100Hz~1kHz。
（2）輸出(chu)電壓：方波(bo) Up-p≤24V，三(san)角(jiao)波(bo) Up-p=6V，正弦(xian)波(bo) Up-p>1V。
2、擴展性能指標要求
頻(pin)率范圍分(fen)段(duan)設置10Hz~100Hz，100Hz~1kHz，1kHz~10kHz；波(bo)(bo)形特性方波(bo)(bo)t r<30us（1kHz，最大輸出時），三角波(bo)(bo)r△<2%，正弦(xian)波(bo)(bo)r～<5%。
