C8051F58X Datasheet, PDF (265/356 Pages) Silicon Laboratories – Programmable hysteresis and response time Configurble as interrupt or reset source Low current

C8051F58x/F59x
25.2. Operational Modes
UART1 provides standard asynchronous, full duplex communication. The UART mode (8-bit or 9-bit) is
selected by the S1MODE bit (SCON1.7). Typical UART connection options are shown in Figure 25.3.
RS-232
RS-232
LEVEL
XLTR
TX
RX ^C8051Fxxx
OR
TX
MCU
RX
TX
C8051Fxxx
RX
Figure 25.3. UART Interconnect Diagram
25.2.1. 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 TX1 pin and received at the RX1 pin. On receive, the eight data
bits are stored in SBUF1 and the stop bit goes into RB81 (SCON1.2).
Data transmission begins when software writes a data byte to the SBUF1 register. The TI1 Transmit Inter-
rupt Flag (SCON1.1) is set at the end of the transmission (the beginning of the stop-bit time). Data recep-
tion can begin any time after the REN1 Receive Enable bit (SCON1.4) is set to logic 1. After the stop bit is
received, the data byte will be loaded into the SBUF1 receive register if the following conditions are met:
RI0 must be logic 0, and if MCE0 is logic 1, the stop bit must be logic 1. In the event of a receive data over-
run, the first received 8 bits are latched into the SBUF1 receive register and the following overrun data bits
are lost.
If these conditions are met, the eight bits of data is stored in SBUF1, the stop bit is stored in RB81 and the
RI1 flag is set. If these conditions are not met, SBUF1 and RB81 will not be loaded and the RI1 flag will not
be set. An interrupt will occur if enabled when either TI1 or RI1 is set.
MARK
SPACE
START
BIT
D0
D1
D2
D3
D4
D5
D6
D7
STOP
BIT
BIT TIMES
BIT SAMPLING
Figure 25.4. 8-Bit UART Timing Diagram
25.2.2. 9-Bit UART
9-bit UART mode uses a total of eleven bits per data byte: a start bit, 8 data bits (LSB first), a programma-
ble ninth data bit, and a stop bit. The state of the ninth transmit data bit is determined by the value in TB81
(SCON1.3), which is assigned by user software. It can be assigned the value of the parity flag (bit P in reg-
ister PSW) for error detection, or used in multiprocessor communications. On receive, the ninth data bit
goes into RB81 (SCON1.2) and the stop bit is ignored.
Rev. 1.2
265