HD6433636SW datasheet(260/418 Pages) RENESAS

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10.3.4

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/received. 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.

(1) Transmit/Receive Formats: Figure 10.5 shows the general format for asynchronous serial

communication.

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), a parity

bit (high or low level), and finally a stop bit (high level), in this order.

In asynchronous data receiving, synchronization is carried out at the falling edge of the start bit.

SCI3 samples data on the 8th pulse of a clock that has 16 times the frequency of one-bit interval,

so each bit of data is latched at its center.

Serial

data

One unit of data (character or frame)

Start

bit

Transmit or receive data

Parity

bit

(MSB)

Stop bit

1 bit

none

1 or 2

bits

7 or 8 bits

Mark

state

(LSB)

Figure 10.5 Data Format in Asynchronous Serial Communication Mode

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