HD6433832S Datasheet, PDF (285/560 Pages) Renesas Technology Corp – single-chip microcomputers

10.4.4 Operation in Asynchronous Mode
In asynchronous communication mode, a start bit indicating the start of communication and a stop
bit indicating the end of communication are added to each character that is sent. In this way
synchronization is achieved for each character as a self-contained unit.
SCI3 consists of independent transmit and receive modules, giving it the capability of full duplex
communication. Both the transmit and receive modules have a double-buffer configuration,
allowing data to be read or written during communication operations so that data can be
transmitted and received continuously.
Transmit/Receive Formats
Figure 10.9 shows the general format for asynchronous serial communication.
Serial
data
(LSB)
Start
bit
1 bit
Transmit or receive data
7 or 8 bits
(MSB)
1
Parity
bit
1 bit
or
none
Stop bit
1 or 2
bits
Mark
state
One unit of data (character or frame)
Figure 10.9 Data Format in Asynchronous Serial Communication Mode
The communication line in asynchronous communication mode normally stays at the high level, in
the “mark” state. SCI3 monitors the communication line, and begins serial data communication
when it detects a “space” (low-level signal), which is regarded as a start bit.
One character consists of a start bit (low level), transmit/receive data (in LSB-first order: starting
with the least significant bit), a parity bit (high or low level), and finally a stop bit (high level), in
this order.
In asynchronous data receiving, synchronization is with the falling edge of the start bit. SCI3
samples data on the 8th pulse of a clock that has 16 times the frequency of the bit rate, so each bit
of data is latched at its center.
Table 10.16 shows the 12 transmit/receive formats formats that can be selected in asynchronous
mode. The format is selected in the serial mode register (SMR).
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