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有時候(hou)我們(men)的(de)(de)代碼會(hui)(hui)跑飛,這個(ge)時候(hou)基(ji)本上(shang)是(shi)一(yi)切推到重來.”推倒(dao)重來”在計算機(ji)術語上(shang)稱(cheng)為復(fu)位(wei)(wei)(wei)(wei)(wei).復(fu)位(wei)(wei)(wei)(wei)(wei)需(xu)(xu)要硬件(jian)的(de)(de)支持(chi)(chi),復(fu)位(wei)(wei)(wei)(wei)(wei)電路(lu)就是(shi)在單片(pian)機(ji)的(de)(de)復(fu)位(wei)(wei)(wei)(wei)(wei)管腳上(shang)產生一(yi)個(ge)信號，俗稱(cheng)復(fu)位(wei)(wei)(wei)(wei)(wei)信號.這個(ge)信號需(xu)(xu)要持(chi)(chi)續一(yi)定的(de)(de)時間,單片(pian)機(ji)收到該信號之后就會(hui)(hui)復(fu)位(wei)(wei)(wei)(wei)(wei),從頭執行。

復位原理:

那么復位(wei)(wei)的原理(li)是什么, 其實很簡(jian)單,復位(wei)(wei)的工作其實是把寄存器的數值加載為(wei)默認值，,即恢復到開機的狀態(tai).由于(yu)單片機在運算過程(cheng)中受外界干擾造成寄存器中數據混亂不能(neng)使(shi)其正常繼(ji)續執行程(cheng)序(稱死機)或單片機的指(zhi)令不按照程(cheng)序執行而指(zhi)向了未(wei)知位(wei)(wei)置(zhi)(俗(su)稱跑飛)，這(zhe)時候(hou)就需要單片機復位(wei)(wei)一下，以使(shi)程(cheng)序重新開始運行.

復(fu)位電(dian)路的設計:

復位電(dian)路的(de)原理是單片機RST引腳接(jie)收到2US以(yi)上的(de)電(dian)平信號，只要(yao)保證(zheng)電(dian)容的(de)充放電(dian)時間大于2US，即可(ke)實(shi)現復位，所(suo)以(yi)電(dian)路中的(de)電(dian)容值是可(ke)以(yi)改變的(de)。如何實(shi)現呢,下面是幾種常見的(de)復位電(dian)路:

第(di)一種,復(fu)位電路

上(shang)電(dian)(dian)(dian)瞬間，由于(yu)電(dian)(dian)(dian)容(rong)(rong)兩端(duan)的(de)(de)電(dian)(dian)(dian)壓不能發(fa)生(sheng)突變，所以電(dian)(dian)(dian)容(rong)(rong)兩端(duan)的(de)(de)電(dian)(dian)(dian)位都是VCC(此時充(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流(liu)最大(da)，電(dian)(dian)(dian)容(rong)(rong)相當于(yu)短路(lu))，即(ji)RST是高(gao)電(dian)(dian)(dian)平(ping)，而隨著VCC通過RC電(dian)(dian)(dian)路(lu)對電(dian)(dian)(dian)容(rong)(rong)充(chong)電(dian)(dian)(dian)，當電(dian)(dian)(dian)容(rong)(rong)兩端(duan)的(de)(de)電(dian)(dian)(dian)壓達到VCC時，電(dian)(dian)(dian)容(rong)(rong)相當于(yu)斷路(lu)(此時電(dian)(dian)(dian)容(rong)(rong)充(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流(liu)為(wei)0，即(ji)隔直(zhi)流(liu))，RST的(de)(de)電(dian)(dian)(dian)平(ping)為(wei)低電(dian)(dian)(dian)平(ping)，單片機正常工作。

第二種復位電路:

上電(dian)(dian)(dian)(dian)(dian)瞬間，由(you)于電(dian)(dian)(dian)(dian)(dian)容(rong)兩(liang)端(duan)的電(dian)(dian)(dian)(dian)(dian)壓不能發生突變，所以電(dian)(dian)(dian)(dian)(dian)容(rong)兩(liang)端(duan)的電(dian)(dian)(dian)(dian)(dian)位都是GND，即RST是低電(dian)(dian)(dian)(dian)(dian)平，而隨著VCC通過RC電(dian)(dian)(dian)(dian)(dian)路(lu)對電(dian)(dian)(dian)(dian)(dian)容(rong)充電(dian)(dian)(dian)(dian)(dian)，當電(dian)(dian)(dian)(dian)(dian)容(rong)兩(liang)端(duan)的電(dian)(dian)(dian)(dian)(dian)壓達到VCC時，RST的電(dian)(dian)(dian)(dian)(dian)平為高電(dian)(dian)(dian)(dian)(dian)平，單(dan)片機(ji)正常工作。

手動復位電路：

手動平復位電路

該電(dian)路(lu)同時也是一個(ge)上電(dian)高(gao)電(dian)平復(fu)位(wei)電(dian)路(lu)。單片機(ji)正常工作時，如果按下按鍵(jian)S1，復(fu)位(wei)引腳RST得(de)到高(gao)電(dian)平，從(cong)而實現復(fu)位(wei)。