Operational Modes; 8-Bit Uart; Figure 22.3. Uart Interconnect Diagram; Figure 22.4. 8-Bit Uart Timing Diagram - Silicon Laboratories C8051F12 Series Manual

8k isp flash mcu
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C8051F120/1/2/3/4/5/6/7 C8051F130/1/2/3

22.2. 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 below.

22.2.1. 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:
RI1 must be logic 0, and if MCE1 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
START
BIT
SPACE
BIT TIMES
BIT SAMPLING
RS-232
TX
MCU
RX

Figure 22.3. UART Interconnect Diagram

D0
D1
D2

Figure 22.4. 8-Bit UART Timing Diagram

TX
RS-232
C8051Fxxx
LEVEL
RX
XLTR
OR
TX
C8051Fxxx
RX
D3
D4
D5
D6
Rev. 1.4
STOP
D7
BIT
301

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