前言

DS2450是一線式4通道逐次逼近式A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" 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title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器" title="A/D轉換器">A/D轉換器，其輸入電壓范圍,、轉換精度位數,、報警門限電壓可編程；每個通道有各自的存儲器以存儲電壓范圍設置,、轉換結果,、門限電壓等參數；普通方式下串行通信速率達16.3kbps,，超速工作時速率達142kbps,，片內16位循環(huán)冗余校驗碼生成器可用于檢測通信的正確性；DS2450采用8引腳SOIC小體積封裝形式,，既可用單5V電源供電,，也可采用寄生電源方式供電。電路正常工作時僅消耗2.5mW功率,，不工作時消耗25μW,。多個DS2450或其他功能的具有MicroLAN接口的一線式芯片可以并聯，CPU只需一根端口線就能與諸多一線式芯片通信,，占用微處理器的端口較少,，可節(jié)省大量的引線和邏輯電路。

2 DS2450的引腳排列和內部結構

DS2450為8引腳SOIC型封裝,，其管腳功能如下：

1腳（VDD）：工作電源接入端
2腳（N.C）：空引腳
3腳（DATA）：串行數據輸入/輸出端
4腳（GND）：接地端
5腳（AIN－A）：A路模擬電壓輸入端
6腳（AIN－B）：B路模擬電壓輸入端
7腳（AIN－C）：C路模擬電壓輸入端
8腳（AIN－D）：D路模擬電壓輸入端
 

DS2450的內部結構如圖1所示,。光刻ROM中的64位序列號是出廠前被光刻好的，它可以看作是該DS2450的地址序列碼,；64位光刻ROM的排列是：開始8位（20H）是產品類型標號,，接著的48位是該DS2450自身的序列號，最后8位是前面56位的循環(huán)冗余校驗碼（CRC=X8＋X5＋X4＋1）,。光刻ROM的作用是使每一個一線式器件的地址都各不相同,，以便實現一根總線上掛接多個一線式電路。

對于一線端口,，在ROM功能建立之前,，其它功能是無法實現的。總線控制器必須首先通過DATA引腳對DS2450提供7個ROM功能控制命令（8位）之一：（1）讀ROM,，命令字[33H],；（2）匹配ROM[55H]；（3）搜索ROM[F0H],；（4）跳過ROM[CCH],；（5）條件搜索ROM[ECH]；（6）超速跳過ROM[3CH],；（7）超速匹配ROM[69H],。其中，超速跳過ROM或超速匹配ROM命令執(zhí)行后,，串行通信速率可高達142kbps,。如果多個器件連接在一線上，這些命令對每個器件的64位ROM部分進行操作,，并挑選出一個特定的器件,。對選中的DS2450，執(zhí)行下一步的A/D轉換控制命令以及讀寫存儲器的命令,，所有命令或數據的讀/寫均從最低位開始,。

3 存儲器組織方式

DS2450內部有24個地址毗連的8位存儲器，可將其分成3頁,，每頁8字節(jié),。DS2450的存儲器組織方式及各位含義如表1所示（高位地址為00H）。

第0頁為A/D轉換結果存儲器,，每個通道占2個字節(jié)16位,，芯片上電復位時該頁清0；其中00H,、01H存儲A通道轉換結果,，LSBA為最低位,，MSBA為最高位,；02H、03H存儲B通道轉換結果;04H,、05H存儲C通道轉換結果;06H,、07H存儲D通道轉換結果，對應位含義與A通道相同,。

第1頁為A/D轉換控制與狀態(tài)存儲器,，08H、09H對應于A通道,，其余通道依次類推,，各位含義相同。RC3、RC2,、RC1,、RC0的組合控制A/D轉換的精度位數，0000為16位,、0001為1位,、……、1111為15位,；特別值得注意的是,，若控制轉換精度不足16位，則在轉換結果的“低位”補0,，湊足16位,，因此讀出結果的16位值中,哪些是有效位與RC3、RC2,、RC1,、RC0的組合有關。對于用作模擬量輸入的通道,，輸出使能位OE必須為0,，否則模擬輸入不被接受，轉換結果始終全為0,，而此時輸出控制位OC可以不必關心,。不用作模擬量輸入的通道可以作為漏極開路的數字輸出端，外接上拉電阻器和工作電源,，在輸出使能位OE=1時,，若輸出控制位OC寫入1，則輸出高電平,，OC寫入0,，則輸出低電平。IR控制輸入電壓范圍,，IR=1時模擬輸入高限為5.10V,，IR=0時輸入高限為2.55V。AEH,、AEL分別為高,、低門限電壓報警允許控制端；AFH,、AFL分別為模擬輸入是否超過規(guī)定的高門限,、低于規(guī)定的低門限的狀態(tài)指示位，若輸入超限,，相應位自動置1,。上電復位標志位POR與通道無關,，上電復位時4個POR自動置1，說明控制字和門限值等未準備好,，該位可用軟件清0,。表中為0的位無效，讀出時始終為0且不能寫入1,。DS2450上電復位時,，默認的控制/狀態(tài)數據的低位為08H、高位為8CH,，即4個通道均作為模擬輸入通道,、8位轉換精度、輸入高限2.55V,、允許高低限報警,。

第2頁為各通道輸入高/低限報警值存儲器，10H存放A通道低門限8位報警值,、11H存放A通道高門限8位報警值,，其余通道依次類推，各位含義相同,。在判斷是否超限時,，只將存儲的門限值與轉換結果的高8位進行比較，然后自動改變AFH,、AFL的狀態(tài),。上電復位時，高限值自動設置為FFH,，低限值自動設置為00H,。

4 轉換與讀/寫控制

4．1轉換控制

通過DS2450的DATA端串行送出轉換命令字[3CH]，隨后送出通道選擇字和預置控制字,，啟動A/D轉換器進行轉換,。DS2450的通道選擇字和預置控制字的各位含義如表2所示。

在通道選擇字中,，對應位為1表示該通道參與轉換,。同時選擇多個通道時，其轉換順序為A→B→C→D,，未選中的通道被跳過,。其A/D轉換的時間可用下式近似計算：轉換時間=通道數×轉換精度位數×80μs＋160μs,。當所有通道轉換完畢,，發(fā)讀存儲器命令可以獲得轉換結果和對應的狀態(tài)。
 

預置控制字可以對相應通道的轉換結果存儲器進行預置,。SET,、CLR=00,，不預置，保持上次轉換值,；SET,、CLR=01，轉換前預置為全0,；SET,、CLR=10，預置為全1,；SET,、CLR=11，無效組合,。