單項選擇題

MCS-51單片機串行口接收數(shù)據(jù)的次序是下述的順序()。
(1)接收完一幀數(shù)據(jù)后,硬件自動將SCON的R1置1       
(2)用軟件將RI清零 
(3)接收到的數(shù)據(jù)由SBUF讀出    
(4)置SCON的REN為1,外部數(shù)據(jù)由RXD輸入 

A.(1)(2)(3)(4)
B.(4)(1)(2)(3)
C.(4)(3)(1)(2)
D.(3)(4)(1)(2)

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