The data to be transmitted is placed in the output register ( SERDAT ). Above the data bits, 1 bits must be added as stop bits. Normally, either one or two stop bits are sent. The transmission of the start bit is independent of the contents of this register. One start bit is automatically generated before the first data bit (bit 0) is sent. Writing this register starts the data transmission. If this register is written with all zeros, no data transmission is initiated.