【導讀】設計一個具有特定功能的電子鐘。該電子鐘上電或按鍵復位后能自動顯示系統(tǒng)提示符“P.”，進入時鐘準備狀態(tài)；第一次按電子鐘啟動/調整鍵，電子鐘從0時0分0秒開始運行，進入時鐘運行狀態(tài)；再次按電子鐘啟動/調整鍵，則電子鐘進入時鐘調整狀態(tài)，此時可利用各調整鍵調整時間，調整結束后可按啟動/調整鍵再次進入時鐘運行狀態(tài)。設計一個能夠測量矩形波信號的頻率、周期、脈寬、占空比的頻率計。將AT89S52的串行口擴展成并行口,外接LED數碼管顯示器；P1口外接四個按鍵A、B、C、D。、以上兩個課題可以任選其一或全選，學生也可以自定課題；、計算機打印《單片機技術》課程設計說明書一份；參照“《單片機技術》課程設計說明書正文主要內容”文件。此電子鐘嚴格按照要求設計，最終達到預期的效果，能夠正確顯示“P”點以及時分秒的計時，算是一次比較成功的設計了。、調整狀態(tài)，按偶數次A鍵進入，在此狀態(tài)下，按A、B、C、D鍵均有效。

　　

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