SH7021 datasheet(381/509 Pages) RENESAS

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RENESAS 366

13.3.2

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 SCI 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 13.2 shows the general format of asynchronous serial communication. In asynchronous

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

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 SCI synchronizes on the falling edge of the start

bit. The SCI 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.

0/1

(LSB)

(MSB)

Serial

data

Start

bit

1 bit

Transmit/receive data

7 or 8 bits

One unit of communication (characters or frames)

Idling (mark state)

Parity

bit

Stop

bit

1 or

no bit

1 or

2 bits

Figure 13.2 Data Format in Asynchronous Communication (Example: 8-bit data with

parity and two stop bits)

SH7021 Datasheet(PDF) 381 Page - Renesas Technology Corp