W79E825A Datasheet, PDF (81/127 Pages) Winbond – 8-BIT MICROCONTROLLER

W79E825A/824A/823B/822B Data Sheet
Fcpu
1/12 1/4
SM2 ⁰
1
RI
REN
RXD
P1.1 Alternate
Input Function
Write to
SBUF
TX START
Internal
Data Bus
TX SHIFT
Transmit Shift Register
PARIN
LOAD
CLOCK
SOUT
RXD
P1.1 Alternate
Output Function
TX CLOCK
TI
Serial Interrupt
RX CLOCK
RI
SHIFT CLOCK
RX START
LOAD SBUF
RX SHIFT
Serial Controllor
CLOCK
PAROUT
SIN
TXD
P1.0 Alternate
Output Function
SBUF
Read SBUF
Internal
Data Bus
Figure 16-1: Serial Port Mode 0
The TI flag is set high in C1 following the end of transmission of the last bit. The serial port will receive
data when REN is 1 and RI is zero. The shift clock (TxD) will be activated and the serial port will latch
data on the rising edge of shift clock. The external device should therefore present data on the falling
edge on the shift clock. This process continues till all the 8 bits have been received. The RI flag is set
in C1 following the last rising edge of the shift clock on TxD. This will stop reception, till the RI is
cleared by software.
16.2 MODE 1
In Mode 1, the full duplex asynchronous mode is used. Serial communication frames are made up of
10 bits transmitted on TXD and received on RXD. The 10 bits consist of a start bit (0), 8 data bits (LSB
first), and a stop bit (1). On received, the stop bit goes into RB8 in the SFR SCON. The baud rate in
this mode is variable. The serial baud can be programmed to be 1/16 or 1/32 of the Timer 1 overflow.
Since the Timer 1 can be set to different reload values, a wide variation in baud rates is possible.
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 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 8 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 10th rollover of the divide-by-16 counter after a write to SBUF.
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Publication Release Date: February 21, 2008
Revision A9