•Mode 0:8-Bit Shift
Register Mode. Terms RXD & TXD are
misleading in this mode. RXD line is used for both input and output. TXD line serves as the clock.
•Eight bits are
transmitted and received with the LSB first. Baud Rate is 1/12 of on-chip oscillator frequency.
•Transmission is initiated by any instruction that writes data to SBUF. Data are shifted out on RXD line with clock pulses sent out by the TXD line. Each transmitted bit is valid on the RXD pin for one machine cycle. E.g.,
MOV SBUF, A
•Reception is initiated when the receiver enable bit (REN) is 1 and the receive interrupt bit (RI) is 0. REN is set
at the beginning of the program, and
then clear RI to begin a data input
operation. The clocking of data into serial port occurs on the positive edge of TXD.