W77E058A Datasheet, PDF (67/87 Pages) Winbond – 8-BIT MICROCONTROLLER

W77E058A
After shifting in 9 data bits, there is one more shift to do, after which the SBUF and RB8 are loaded
and RI is set. However certain conditions must be met before the loading and setting of RI can be
done.
1. RI must be 0 and
2. Either SM2 = 0, or the received stop bit = 1.
If these conditions are met, then the stop bit goes to RB8, the 8 data bits go into SBUF and RI is set.
Otherwise the received frame may be lost. After the middle of the stop bit, the receiver goes back to
looking for a 1-to-0 transition on the RxD pin.
14.4 Mode 3
This mode is similar to Mode 2 in all respects, except that the baud rate is programmable. The user
must first initialize the Serial related SFR SCON before any communication can take place. This
involves selection of the Mode and baud rate. The Timer 1 should also be initialized if modes 1 and 3
are used. In all four modes, transmission is started by any instruction that uses SBUF as a destination
register. Reception is initiated in Mode 0 by the condition RI = 0 and REN = 1. This will generate a
clock on the TxD pin and shift in 8 bits on the RxD pin. Reception is initiated in the other modes by the
incoming start bit if REN = 1. The external device will start the communication by transmitting the start
bit.
Timer 1
Overflow
Timer 2 Overflow
(for Serial Port 0 only)
2
Write to
SBUF
TB8
Internal
Data Bus
SMOD=
(SMOD_1) ⁰
1
TCLK _{0 1}
16
TX START TX SHIFT
TX CLOCK
TI
RCLK
01
16
SAMPLE
1-TO-0
DETECTOR
SERIAL
CONTROLLER ^RI
RX CLOCK
RX
START
LOAD
SBUF
RX SHIFT
STOP
D8
PARIN
START ^SOUT
LOAD
CLOCK
Transmit Shift Register
TXD
Serial Port
Interrupt
Read
SBUF
RXD
BIT
DETECTOR
CLOCK
PAROUT
SBUF
SIN
D8
RB8
Receive Shift Register
Internal
Data
Bus
Figure 23. Serial Port Mode 3
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Publication Release Date: April 17, 2007
Revision A10