Hi friends: Have to ask you other questions. Right now I am running my program on my experiment board. After resetting AT89C51, Should the initial values of P0 port be 0Xff? Why mine are 0x00? Should I connect P0 port with pull up resistors even I want to use bus mode for P0 and P2 ports? If I connect P0 port with pull up resistors, may I address P0 port by bus mode? About MT8888C (which is with Intel interface): yesterday the AT89C51 on my experiment board successfully communicate with MT8888C. But today they don't work for me. According to my checking, AT89C51 with above question and the data port of MT8888C are all low (should they be high or not?). I control MT8888C by P0 and P2 Port of AT89C51 using Bus mode, P0.0-P0.3 connect to D0-D3, P2.0 connect to RS0, P2.1 connect to CS of MT8888C, WR and RD of AT89C51 connect to WR and RD of MT8888C, respectively. Are you sure I am right with above hardware setting or should it be wrong with software? I am really lost and confused……… If any friends know any possible answers about those simple questions, please let me know. My sincerely thanks in advance.