HD6417706 RENESAS [Renesas Technology Corp], HD6417706 Datasheet - Page 420

• Manufacturer Part Number: HD6417706
• Description: Renesas 32-Bit RISC Microcomputer Super RISC engine Family/SH7700 Series
• Manufacturer: RENESAS [Renesas Technology Corp]

14.4.1
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.
Rev. 4.00, 03/04, page 374 of 660
Example: 8-bit data with parity and two stop bits
Serial
Operation in Asynchronous Mode
data
1
1 bit
Start
Figure 14.5 Data Format in Asynchronous Communication
bit
0
(LSB)
D 0
D 1
One unit of communication data (character or frame)
D 2
Transmit/receive data
D 3
7 or 8 bits
D 4
D 5
D 6
(MSB)
D 7
Parity
no bit
1 or
0/1
bit
Idling (marking)
1
Stop
2 bits
1 or
bit
1
1