SH7055S Datasheet, PDF (522/1002 Pages) Renesas Technology Corp – Renesas 32-Bit RISC Microcomputer SuperH RISC engine Family/SH7000 Series

15.3.2 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 15.2 shows the general format of asynchronous serial communication. In asynchronous
serial communication, the communication line is normally held in the marking (high) state. The
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.
1
(LSB)
(MSB)
Idling (marking)
1
Serial _{0 D0 D1 D2 D3 D4 D5 D6 D7 0/1 1}
1
data
Start
Parity Stop
bit
bit
bit
Transmit/receive data
1 bit
7 or 8 bits
1 or 1 or
no bit 2 bits
One unit of communication data (character or frame)
Figure 15.2 Data Format in Asynchronous Communication (Example: 8-bit Data with
Parity and Two Stop Bits)
Rev.2.0, 07/03, page 484 of 960