SH7125_08 Datasheet, PDF (464/774 Pages) Renesas Technology Corp – Renesas 32-Bit RISC Microcomputer SuperH™ RISC engine Family

Section 12 Serial Communication Interface (SCI)
12.4.2 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. Both the transmitter and receiver have a double-buffered structure so that data can be
read or written during transmission or reception, enabling continuous data transfer.
Figure 12.2 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 at 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
Idle state
(mark state)
1
Serial
0 D0 D1 D2 D3 D4 D5 D6 D7 0/1 1
1
data
Start
bit
Transmit/receive data
Parity Stop bit
bit
1 bit
7 or 8 bits
1 bit or 1 or 2 bits
none
One unit of transfer data (character or frame)
Figure 12.2 Example of Data Format in Asynchronous Communication
(8-Bit Data with Parity and Two Stop Bits)
Rev. 4.00 Jul. 25, 2008 Page 444 of 750
REJ09B0243-0400