SH7014 Datasheet, PDF (367/754 Pages) Renesas Technology Corp – 32-Bit RISC Microcomputer

12. Serial Communication Interface (SCI)
12.3.2 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 12.2 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 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)
Idling (marking state)
(MSB)
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 (characters or frames)
Figure 12.2 Data Format in Asynchronous Communication
(Example: 8-bit Data with Parity and Two Stop Bits)
Rev.5.00 Sep. 27, 2007 Page 333 of 716
REJ09B0398-0500