1、P89V51RD2 單片機(jī)看門(mén)狗的使用方法P89V51RD2 具有一個(gè)可編程的看門(mén)狗定時(shí)器（WDT），可用于系統(tǒng)故障安全保護(hù)，防止死鎖和自動(dòng)恢復(fù)。WDT 在CPU 落入運(yùn)行失控的情況下可作為一種恢復(fù)的方法。P89V51RD2 有兩個(gè)特殊功能寄存器 WDTC（地址 0 xC0）和 WDTD（地址 0 x85）用于看門(mén)狗功能，有關(guān)這兩個(gè)寄存器的詳細(xì)注解參見(jiàn)P89V51RD2 器件手冊(cè)。WDT 的溢出周期可由下式計(jì)算得出：T =（255 WDTD）344064*1/fOSC，此處 WDTD 為 WDTD 寄存器的裝載值，fOSC 是系統(tǒng)時(shí)鐘。每經(jīng)過(guò) 344, 064 個(gè)振蕩周期，WDT 寄存器加 1

2、。當(dāng)向 WDTD 裝載 0 值時(shí)看門(mén)狗獲得最大的溢出周期 7.90s；當(dāng)向 WDTD 裝載 0 xFE 時(shí)看門(mén)狗獲得最小的溢出周期 31.11ms；表 1 給出當(dāng) fOSC 為 11.0592M 時(shí)不同溢出周期對(duì)應(yīng)的 WDTD 裝載值的簡(jiǎn)表。若使用其它的晶振或想得到其它的溢出周期可根據(jù)公式自行計(jì)算。表 1 P89V51RD2 看門(mén)狗溢出周期取樣P89V51RD2 看門(mén)狗的啟動(dòng)和關(guān)閉通過(guò) WDTC 寄存器的SWDT 位實(shí)現(xiàn)，該位被置位啟動(dòng)看門(mén)狗，該位被清零時(shí)關(guān)閉看門(mén)狗。要使能 WDT 復(fù)位，用戶必須將WDTC 寄存器的 WDRE 位置 1。當(dāng)看門(mén)狗使能且發(fā)生溢出時(shí)，它將會(huì)在 RST 腳產(chǎn)生一個(gè)復(fù)

3、位脈沖執(zhí)行復(fù)位。為避免看門(mén)狗溢出產(chǎn)生復(fù)位，用戶需要定期執(zhí)行“喂作。執(zhí)行“喂作時(shí)，在向 WDTD 寫(xiě)入重裝值后，必須立即執(zhí)行看門(mén)狗定時(shí)器刷新（置位WDT）才能將數(shù)據(jù)成功寫(xiě)入 WDTD 寄存器中，否則數(shù)據(jù)不能被寫(xiě)入。以下實(shí)驗(yàn)例程使用了 WDT 的定時(shí)和復(fù)位功能，系統(tǒng)在上電復(fù)位后 LED2 點(diǎn)亮一下即熄滅，接下來(lái)實(shí)現(xiàn)LED1 閃動(dòng)控制。若按下KEY 鍵，則啟動(dòng)看門(mén)狗定時(shí)器并打開(kāi)看門(mén)狗復(fù)位輸出使能，若掉“喂狗子程序”，4s 后可觀察到系統(tǒng)復(fù)位（LED2 被點(diǎn)亮一下）；若不“喂狗子程序”則會(huì)看到 LED1 一直在閃動(dòng)而LED2 一直熄滅，說(shuō)明程序一直在正常運(yùn)行而未發(fā)生看門(mén)狗復(fù)位。/*文件名:WDT_te

4、st.c周立功單片機(jī)P89V51RD2 看門(mén)狗C 語(yǔ)言演示程序2004/6/28*:*功能:*日期:*/#include sfrsfrWDTC = 0 xC0;WDTD = 0 x85;/ 看門(mén)狗定時(shí)器控制寄存器/ 看門(mén)狗定時(shí)數(shù)據(jù)/重裝數(shù)據(jù)控制寄存器- 1 -WDTD 裝載值看門(mén)狗溢出周期0 xFE31.11ms0 xDD1.0s0 xBD2.0s0 x9D3.0s0 x7D4.0s0 x5D5.0s0 x3D6.0s0 x1D7.0s0 x017.90ssbit sbitsbitKEY = P33; LED1= P10;LED2= P11;main()j, i;char flag = 0;L

5、ED2 = 0; for(i=0;i=5)WDTD = 0 x80; WDTC = WDTC|0 x02; i=0; for(j=0;j4000;j+); i+;while(1);/檢查程序是否運(yùn)行指示燈/啟動(dòng)看門(mén)狗定時(shí)器,使能看門(mén)狗定時(shí)器復(fù)位裝入重裝載值執(zhí)行裝載指令/定時(shí)喂喂狗子程序作裝入重載值執(zhí)行裝載指令/延時(shí)/*文件名:WDT_test.asm周立功單片機(jī)P89V51RD2 看門(mén)狗匯編演示程序2004/6/28*:*功能:*日期:*/$NOMOD51$INCLUDE(REG51.INC)WDTCWDTDDATADATA0C0H085H;定義 WDTC 看門(mén)狗定時(shí)器控制寄存器的地址;定義

6、WDTD 看門(mén)狗定時(shí)器數(shù)據(jù)/重裝寄存器地址- 2 -KEYLED1 LED2BITBIT BITP3.3P1.0 P1.1;定義按鍵端口;定義指示燈端口0000HMAINAJMP0100H LED2 DELAY LED2 LED1 DELAYKEY,CIRCLEKEY,FEED WDTCONMAIN:CPL CALL CPL CPL CALL JBJBAJMPCIRCLE:;有鍵按下后則等待看門(mén)狗復(fù)位，無(wú)鍵按下使LED1 閃爍;調(diào)用喂狗子程序;= = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =;啟動(dòng)看門(mén)狗定

7、時(shí)器分支程序;= = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =WDTCON: MOVMOV MOV MOV ORLAJMPA,#09H WDTC,A A,#80H WDTD,A WDTC,#02HCIRCLE;啟動(dòng)看門(mén)狗定時(shí)器;寫(xiě)入定時(shí)初值;執(zhí)行定時(shí)器刷新;= = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =;WDT 看門(mén)狗喂狗分支程序;= = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =FEED:MOV MOV ORLAJMPA,#80H WDTD,A WDTC,#02HCIRCLE;寫(xiě)入定時(shí)初值;執(zhí)行定時(shí)器刷新;= = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =;延時(shí)子程序;= = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =DELAY: MOV DELA