SH7708 datasheet(384/633 Pages) RENESAS

384 / 633 page

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13.3.2

Operation in Asynchronous Mode

In 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 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 data (character or frame)

Idle (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 2 Stop Bits)

Transmit/Receive Formats: Table 13.11 lists the 12 communication formats that can be selected

in asynchronous mode. The format is selected by settings in the serial mode register (SCSMR).

SH7708 Datenblatt(PDF) 384 Page - Renesas Technology Corp