高精度時(shí)鐘程序 JANSR2N7422

   圖6-15所示為高精度時(shí)鐘程序,秒脈沖特殊存儲(chǔ)器SM0.5作為秒發(fā)生器,用于計(jì)數(shù)器C51的計(jì)數(shù)脈沖信號(hào)。當(dāng)計(jì)數(shù)器C51的計(jì)數(shù)累計(jì)值達(dá)到設(shè)定值60次時(shí)(即為1min時(shí)),計(jì)數(shù)器位置“1”,即C51的常開觸點(diǎn)閉合,該信號(hào)將作為計(jì)數(shù)器62的計(jì)數(shù)脈沖信號(hào);計(jì)數(shù)器C51的另一常開觸點(diǎn)使計(jì)數(shù)器αl復(fù)位(稱為自復(fù)位式)后,使計(jì)數(shù)器C51從0開始重新計(jì)數(shù)。相似地,計(jì)數(shù)器α2計(jì)數(shù)到60次時(shí)(即為1h時(shí)),其兩個(gè)常開觸點(diǎn)閉合,一個(gè)作為計(jì)數(shù)器C53的計(jì)數(shù)脈沖信號(hào),另一個(gè)使計(jì)數(shù)器C52自復(fù)位,又重新開始計(jì)數(shù);計(jì)數(shù)器C53計(jì)數(shù)到24次時(shí)(即為1天),其常開觸點(diǎn)閉合,使計(jì)數(shù)器C53自復(fù)位,又重新開始計(jì)數(shù),從而實(shí)現(xiàn)時(shí)鐘功能。輸入信號(hào)IO。1、IO,2用于建立期望的時(shí)鐘設(shè)置,即調(diào)整分針、時(shí)針。