D12320VF25V Datasheet, PDF (496/1146 Pages) Renesas Technology Corp – Old Company Name in Catalogs and Other Documents

Section 12 Serial Communication Interface (SCI)
12.3.2 Operation in Asynchronous Mode
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 communication line is usually held in the mark state
(high level). The SCI monitors the communication 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.
Idle state
(mark state)
1
LSB
MSB
1
Serial _{0 D0 D1 D2 D3 D4 D5 D6 D7 0/1 1}
1
data
Start
bit
Transmit/receive data
Parity Stop bit(s)
bit
1 bit
7 or 8 bits
1 bit, 1 or
or none 2 bits
One unit of transfer data (character or frame)
Figure 12.2 Data Format in Asynchronous Communication
(Example with 8-Bit Data, Parity, Two Stop Bits)
Rev.7.00 Feb. 14, 2007 page 462 of 1108
REJ09B0089-0700