Datasheet

Section 13 Serial Communication Interface (SCI)

Rev. 3.00 Sep. 28, 2009 Page 271 of 710

REJ09B0384-0300

13.4 Operation in Asynchronous Mode

Figure 13.2 shows the general format for asynchronous serial communication. One frame consists

of a start bit (low level), followed by transmit/receive data, a parity bit, 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, and when it goes to the space state (low

level), recognizes a start bit and starts serial communication. Inside the SCI, the transmitter and

receiver are independent units, enabling full-duplex communication. Both the transmitter and the

receiver also have a double-buffered structure, so that data can be read or written during

transmission or reception, enabling continuous data transfer and reception.

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

Serial

data

Parity

bit

1 bit 1 or 2 bits7 or 8 bits 1 bit or

none

One unit of transfer data (character or frame)

Figure 13.2 Data Format in Asynchronous Communication

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