w77e58 Winbond Electronics Corp America, w77e58 Datasheet - Page 66

• Manufacturer Part Number: w77e58
• Description: 8 Bit Microcontroller
• Manufacturer: Winbond Electronics Corp America

MODE 2
This mode uses a total of 11 bits in asynchronous full-duplex communication. The functional
description is shown in the figure below. The frame consists of one start bit (0), 8 data bits (LSB first),
a programmable 9th bit (TB8) and a stop bit (0). The 9th bit received is put into RB8. The baud rate is
programmable 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 C1 following the first roll-over of the divide by 16 counter. The next bit is placed on TxD pin at C1
following the next rollover of the divide by 16 counter. Thus the transmission is synchronized to the
divide by 16 counter, and not directly to the write to SBUF signal. After all 9 bits of data are
transmitted, the stop bit is transmitted. The TI flag is set in the C1 state after the stop bit has been put
out on TxD pin. This will be at the 11th rollover of the divide by 16 counter after a write to SBUF.
Reception is enabled only if REN is high. The serial port actually starts the receiving of serial data,
with the detection of a falling edge on the RxD pin. The 1-to-0 detector continuously monitors the RxD
line, sampling it at the rate of 16 times the selected baud rate. When a falling edge is detected, the
divide by 16 counter is immediately reset. This helps to align the bit boundaries with the rollovers of
the divide by 16 counter. The 16 states of the counter effectively divide the bit time into 16 slices. The
bit detection is done on a 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 rejection feature of the serial port.
(SMOD_1)
SMOD=
RCLK
TCLK
Overflow
Timer 1
RXD
2
0
SAMPLE
0
0
1
(for Serial Port 0 only)
1
1
DETECTOR
Timer 2 Overflow
1-TO-0
16
16
Write to
SBUF
START
RX CLOCK
TX START
TX CLOCK
CONTROLLER
DETECTOR
RX
SERIAL
Figure 21. Serial Port Mode 1
BIT
Data Bus
TX SHIFT
RX SHIFT
Internal
LOAD
SBUF
- 66 -
TI
RI
Receive Shift Register
CLOCK
SIN
Transmit Shift Register
PAROUT
CLOCK
STOP
START
LOAD
PARIN
D8
Preliminary W77E58
SOUT
SBUF
RB8
Serial Port
SBUF
Interrupt
Read
TXD
Internal
Data
Bus