Actually I intend to design a DLL interface for serial communication supporting MARK and SPACE mode. When the data from outside come, I wish the simulation to put them into the registers of the 8051. However, as mentioned before, the SBUF seems of little use, and I have tried SIN, which I assumed that the value in SBUF would change with it accordingly but found that it was of no help. What should I do to get the data into the registers? Thanks!