w79e532 Winbond Electronics Corp America, w79e532 Datasheet - Page 53

• Manufacturer Part Number: w79e532
• 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.
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.
(SMOD_1)
SMOD=
PTD
SAMPLE
RXD
2
0
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
TX
TB8
RI
TI
- 53 -
CLOCK
SIN
Receive Shift Register
PAROUT
Publication Release Date: November 21, 2005
START
LOAD
CLOCK
D8
STOP
PARIN
Transmit Shift Register
D8
W79E532/W79L532
SOUT
SBUF
RB8
Serial Port
Interrupt
Read
SBUF
TXD
Internal
Data
Revision A5
Bus