HD6412240 RENESAS [Renesas Technology Corp], HD6412240 Datasheet - Page 476

• Manufacturer Part Number: HD6412240
• Description: Renesas 16-Bit Single-Chip Microcomputer H8S Family / H8S/2200 Series
• Manufacturer: RENESAS [Renesas Technology Corp]

Section 12 Serial Communication Interface (SCI)
12.3.2
In asynchronous mode, characters are sent or received, each preceded by a start bit indicating the
start of communication and one or two stop bits indicating the end of communication. Serial
communication is thus carried out with synchronization established on a character-by-character
basis.
Inside the SCI, the transmitter and receiver are independent units, enabling full-duplex
communication. Both the transmitter and the receiver also 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 for asynchronous serial communication.
In asynchronous serial communication, the transmission line is usually held in the mark state (high
level). The SCI monitors the transmission line, and when it goes to the space state (low level),
recognizes a start bit and starts serial communication.
One serial communication character consists of a start bit (low level), followed by data (in LSB-
first order), a parity bit (high or low level), and finally one or two stop bits (high level).
In asynchronous mode, the SCI performs synchronization at the falling edge of the start bit in
reception. The SCI samples the data on the 8th pulse of a clock with a frequency of 16 times the
length of one bit, so that the transfer data is latched at the center of each bit.
Rev.3.00 Mar. 26, 2007 Page 434 of 772
REJ09B0355-0300
Serial
data
1
Operation in Asynchronous Mode
Start
bit
1 bit
0
Figure 12.2 Data Format in Asynchronous Communication
LSB
D0
(Example with 8-Bit Data, Parity, Two Stop Bits)
One unit of transfer data (character or frame)
D1
D2
Transmit/receive data
D3
7 or 8 bits
D4
D5
D6
D7
Parity
bit
1 bit,
or none
MSB
0/1
Stop bit
1
1 or
2 bits
1
Idle state
(mark state)
1