C8051F850-C-GM Datasheet, PDF (305/328 Pages) Silicon Laboratories – Low-Cost 8-bit MCU Family with up to 8 kB of Flash

26.2. Operational Modes
UART0 provides standard asynchronous, full duplex communication. The UART mode (8-bit or 9-bit) is
selected by the S0MODE bit in register SCON.
26.2.1. 8-Bit UART
8-Bit UART mode uses a total of 10 bits per data byte: one start bit, eight data bits (LSB first), and one stop
bit. Data are transmitted LSB first from the TX pin and received at the RX pin. On receive, the eight data
bits are stored in SBUF0 and the stop bit goes into RB8 in the SCON register.
Data transmission begins when software writes a data byte to the SBUF0 register. The TI Transmit
Interrupt Flag is set at the end of the transmission (the beginning of the stop-bit time). Data reception can
begin any time after the REN Receive Enable bit is set to logic 1. After the stop bit is received, the data
byte will be loaded into the SBUF0 receive register if the following conditions are met: RI must be logic 0,
and if MCE is logic 1, the stop bit must be logic 1. In the event of a receive data overrun, the first received
8 bits are latched into the SBUF0 receive register and the following overrun data bits are lost.
If these conditions are met, the eight bits of data is stored in SBUF0, the stop bit is stored in RB8 and the
RI flag is set. If these conditions are not met, SBUF0 and RB8 will not be loaded and the RI flag will not be
set. An interrupt will occur if enabled when either TI or RI is set.
MARK
SPACE
BIT TIMES
START
BIT
BIT SAMPLING
D0
D1
D2
D3
D4
D5
D6
Figure 26.3. 8-Bit UART Timing Diagram
D7
STOP
BIT
Rev. 1.0
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