W78E054D Datasheet, PDF (58/89 Pages) List of Unclassifed Manufacturers – 8-bit microcontroller

W78E054D/W78E052D Data Sheet
best of three basis. The bit detector samples the RxD pin, at the 8th, 9th 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 rejec-
tion 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 8 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.
Timer 1
Overflow
Timer 2
Overflow
1/2
SMOD 0 1
0
1
TCLK
RCLK ⁰
1
1/16
1/16
SAMPLE
1-To-0
DETECTOR
RXD
Write to
SBUF
TX START
TX CLOCK
Transmit Shift Register
1
Internal
Data Bus
0
STOP
PARIN
START ^{SOUT TXD}
LOAD
CLOCK
TX SHIFT
Serial
Controllor ^TI
RX CLOCK
RI
TX START
LOAD SBUF
RX SHIFT
Serial Interrupt
Read SBUF
BIT
DETECTOR
CLOCK PAROUT ^SBUF
SIN
D8
RB8
Receive Shift Register
Internal
Data Bus
Figure 16–2 Serial port mode 1
16.3 MODE 2
This mode uses a total of 11 bits in asynchronous full-duplex communication. The functional descrip-
tion is shown in the figure below. The frame consists of one start bit (0), 8 data bits (LSB first), a pro-
grammable 9th bit (TB8) and a stop bit (1). The 9th bit received is put into RB8. The baud rate is pro-
grammable to 1/32 or 1/64 of the oscillator frequency, which is determined by the SMOD bit in PCON
SFR. Transmission begins with a write to SBUF. The serial data is brought out on to TxD pin at S6P2
following the first roll-over of the divide by 16 counter. The next bit is placed on TxD pin at S6P2 fol-
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Publication Release Date: Jun 9, 2015
Revision A13