Datasheet

Section 12 Serial Communication Interface

Rev.7.00 Dec. 24, 2008 Page 403 of 698

REJ09B0074-0700

12.4 Operation in Asynchronous Mode

Figure 12.5 shows the general format for asynchronous serial communication. One frame consists

of a start bit (low level), followed by data (in LSB-first order), a parity bit (high or low level), and

finally stop bits (high level). In asynchronous serial communication, the transmission line is

usually held in the mark state (high level). The SCI monitors the transmission line. When the

transmission line goes to the space state (low level), the SCI recognizes a start bit and starts serial

communication. Inside the SCI, the transmitter and receiver are independent units, enabling full-

duplex. Both the transmitter and the receiver also have a double-buffered structure, so data can be

read from or written during transmission or reception, enabling continuous data transfer.

LSB

Start

bit

MSB

Idle state

(mark state)

Stop bit

Transmit/receive data

D0 D1 D2 D3 D4 D5 D6 D7 0/1 1 1

1 1

Serial

data

Parity

bit

1 bit 1 or

2 bits

7 or 8 bits

1 bit,

or none

One unit of transfer data (character or frame)

Figure 12.5 Data Format in Asynchronous Communication

(Example with 8-Bit Data, Parity, Two Stop Bits)