w77e58 Winbond Electronics Corp America, w77e58 Datasheet - Page 67

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

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.
(SMOD_1)
SMOD=
div. by 4
div. by 64
div. by 1024 osc/512
Mode
Clock Source
SAMPLE
RXD
2
0
input
osc/2
osc/32
1
DETECTOR
1-TO-0
16
16
Write to
SBUF
RX CLOCK
RX START
TX START
TX CLOCK
CONTROLLER
DETECTOR
SERIAL
BIT
Figure 22. Serial Port Mode 2
Data Bus
Internal
RX SHIFT
SHIFT
LOAD
SBUF
- 67 -
TX
TB8
RI
TI
CLOCK
SIN
Receive Shift Register
PAROUT
START
LOAD
CLOCK
D8
STOP
PARIN
Transmit Shift Register
D8
Preliminary W77E58
Publication Release Date: March 1999
SOUT
SBUF
RB8
Serial Port
Interrupt
Read
SBUF
TXD
Internal
Revision A1
Data
Bus