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SH79F3283
93
Mode2: 9-Bit EUART, Fixed Baud Rate, Asynchronous Full-Duplex
This mode provides the 11 bits full duplex asynchronous communication. The 11 bit consists of one start bit (logical 0), 8 data
bits (LSB first), a programmable 9
th
data bit, and a stop bit (logical 1). Mode 2 supports multiprocessor communications and
hardware address recognition (Refer to Multiprocessor Communication Section for details). When data is transmitted, the 9
th
data bit (TB8 in SCON) can be assigned the value of 0 or 1, for example, the parity bit P in the PSW or used as data/address
flag in multiprocessor communications. When data is received, the 9
th
data bit goes into RB8 and the stop bit is not saved. The
baud rate is programmable to either 1/32 or 1/64 of the system working frequency, as determined by the SMOD bit in PCON.
The functional block diagram is shown below:
SERIAL
CONTROLLER
TX CLOCK
TX START
TX SHIFT
TI
RI
RX CLOCK
LOAD SBUF
RX START
RX SHIFT
TXD
Serial Port Interrupt
PARIN
LOAD
CLOCK
SOUT
CLOCK
SIN
PAROUT
RXD
Read SBUF
Internal
Data Bus
Receive Shift Register
Internal
Data Bus
32
÷
32
÷
1-TO-0
DETECTOR
Write to SBUF
BIT
DETECTOR
D8
SBUF
RB8
Transmit Shift Register
STOP
START
SAMPLE
1
0
2
÷
D8
TB8
SMOD
System Clock
Transmission begins with a “write to SBUF” signal, the “write to SBUF” signal also loads TB8 into the 9
th
bit position of the
transmit shift register. Transmission actually commences at the next system clock following the next rollover in the
divide-by-16 counter (thus, the bit times are synchronized to the divide-by-16 counter, not to the “write to SUBF” signal). The
start bit is firstly put out on TXD pin, then the 9 bits of data is the next. After all 9 bits of data in the transmit shift register are
transmitted, the stop bit is put out on the TXD pin, and the TI flag is set at the same time.
Write to SBUF
Shift CLK
TI
Send Timing of Mode 2
TxD
D8
D0
D1
D2
D3
D4
D5
D6
D7
Start
Stop