SH7018 datasheet(243/431 Pages) RENESAS

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12.3.2

Operation in Asynchronous Mode

In the asynchronous mode, each transmitted or received character begins with a start bit and ends

with a stop bit. Serial communication is synchronized one character at a time.

The transmitting and receiving sections of the SCI1 are independent, so full duplex

communication is possible. The transmitter and receiver are both double buffered, so data can be

written and read while transmitting and receiving are in progress, enabling continuous transmitting

and receiving.

Figure 12.2 shows the general format of asynchronous serial communication. In asynchronous

serial communication, the communication line is normally held in the marking (high) state. The

SCI1 monitors the line and starts serial communication when the line goes to the space (low) state,

indicating a start bit. One serial character consists of a start bit (low), data (LSB first), parity bit

(high or low), and stop bit (high), in that order.

When receiving in the asynchronous mode, the SCI1 synchronizes on the falling edge of the start

bit. The SCI1 samples each data bit on the eighth pulse of a clock with a frequency 16 times the

bit rate. Receive data is latched at the center of each bit.

D1D2D3

0/1

(LSB)

(MSB)

Serial

data

Start

bit

1 bit

Transmit/receive data

7 or 8 bits

One unit of communication data (characters or frames)

Idling (marking state)

Parity

bit

Stop

bit

1 or

no bit

1 or

2 bits

Figure 12.2 Data Format in Asynchronous Communication (Example: 8-bit Data with

Parity and Two Stop Bits)

SH7018 Datasheet(PDF) 243 Page - Renesas Technology Corp