Working mode of 80C51 Serial Port

One , The way 0                                                                                                                                                  The way 0 when , Input mode of serial port synchronous shift register . It is mainly used to expand the input and output of the parallel port . data RXD Pin input or output , The synchronous shift pulse is generated by TXD Pin out . Both sending and receiving are 8 For data , Low first , High position behind . The baud rate is fixed to fosc/12.                                                                                                                        The way 0 Output                                                                                                                                               

  The way 0 Input

Two , The way 1                                                                                                                                                  The way 1 yes 10 Bit data asynchronous communication port .TXD Send pin for data ,RXD Accept feet for data , The format of transmission data is shown in the figure . 

    The way 1 Output ：

                 

The way 1 Input

 

          Set... With software REN by 1 when , Receiver to select baud rate 16 Multiple rate sampling RXD Pin level , detected RXD When there is a negative jump in the input level of the pin , Then the start bit is valid , Input its shift into the shift register , And start receiving the remaining bits of this frame information ,. During reception , Data is moved from the right side of the shift register , When the start bit moves to the leftmost side of the input register , The control circuit performs the last shift . When RI=0, And SM2=0 when , Will receive 9 The first bit of data 8 Bit data loading and receiving SBUF, Ninth entry RB8,b Juxtaposition RB8=1, towards CPU Request interrupt .    Set... With software REN by 1 when , The receiver operates at the selected baud rate 16 Multiple rate sampling RXD Pin level , detected RXD When there is a negative jump in the input level of the pin , Then the start bit is valid , Move it into the input shift register , And start receiving the remaining bits of this frame information . During reception , Data is moved from the right side of the input shift register into , When the initial shift reaches the leftmost side of the input shift register , The control circuit performs the last shift . When RI=0, And SM2=0（ Or the received stop bit is 1） when , Will receive 9 The first bit of data 8 Bit data loading and receiving SBUF, The first 9 position （ Stop bit ） Get into RB8, Juxtaposition RI=1, towards CPU Request interrupt .