SH7706 Datasheet, PDF (440/749 Pages) Renesas Technology Corp – Renesas 32-Bit RISC Microcomputer SuperH™ RISC engine Family/SH7700 Series

Section 14 Serial Communication Interface (SCI)
14.4.1 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 14.5 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.
1
(LSB)
(MSB)
Idling (marking)
1
Serial
data
0
D0
Start
bit
1 bit
D1 D2 D3 D4 D5 D6 D7
0/1 1
1
Parity
bit
Stop
bit
Transmit/receive data
7 or 8 bits
1 or
no bit
1 or
2 bits
One unit of communication data (character or frame)
Example: 8-bit data with parity and two stop bits
Figure 14.5 Data Format in Asynchronous Communication
Rev. 5.00 May 29, 2006 page 392 of 698
REJ09B0146-0500