W925EP01 Datasheet, PDF (57/108 Pages) Winbond – 8-BIT CID MICROCONTROLLER

W925EP01/ W925EP01FG
and 10th counter states. By using a majority 2 of 3 voting system, the bit value is selected. This is
done to improve the noise rejection feature of the serial port. If the first bit detected after the falling
edge of RxD pin, is not 0, then this indicates an invalid start bit, and the reception is immediately
aborted. The serial port again looks for a falling edge in the RxD line. If a valid start bit is detected,
then the rest of the bits are also detected and shifted into the SBUF. 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.
Fosc/2
2
Write to
SBUF
TB8
Internal
Data Bus
SMOD _{0 1}
(PCON.7)
16
16
SAMPLE
1-TO-0
DETECTOR
TX START
TX CLOCK
TX
SHIFT
TI
SERIAL
CONTROLLER _RI
RX CLOCK
RX START
LOAD
SBUF
RX SHIFT
RXD
BIT
DETECTOR
D8
STOP
PARIN
START ^SOUT
LOAD
CLOCK
Transmit Shift Register
TXD
Serial Port
Interrupt
CLOCK
PAROUT
SBUF
SIN
D8
RB8
Receive Shift Register
Read
SBUF
Internal
Data
Bus
Figure 6-10 Serial Port 0 Mode 2
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Publication Release Date: Apr. 10, 2006
Revision A2