SH7760 Datasheet, PDF (628/1345 Pages) Renesas Technology Corp – SuperHTM RISC engine

17.4.2 Operation in Asynchronous Mode
In asynchronous mode, a character that consists of data with a start bit indicating the start of
communication and a stop bit indicating the end of communication is transmitted or received. In
this mode, serial communication is performed with synchronization achieved character by
character.
Inside the SCIF, the transmitter and receiver are independent units, enabling full-duplex
communication. Both the transmitter and receiver have a 128-stage FIFO buffer structure, so that
data can be read or written during transmission or reception, enabling continuous data
transmission and reception.
Figure 17.7 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 SCIF monitors the transmission line, and when it goes to the space state (low level),
recognizes a start bit and starts serial communication.
One character in serial communication consists of a start bit (low level), followed by
transmit/receive data (LSB-first; from the lowest bit), a parity bit (high or low level), and finally
stop bits (high level).
In reception in asynchronous mode, the SCIF synchronizes with the fall of the start bit. Receive
data can be latched at the middle of each bit because the SCIF samples data at the eighth clock
which has a frequency of 16 times the bit rate.
Idle state
(mark state)
1
LSB
MSB
1
Serial
data
0 D0 D1 D2 D3 D4 D5 D6 D7 0/1 1 1
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 17.7 Data Format in Asynchronous Communication
(Example with 8-Bit Data, Parity, and Two Stop Bits)
Rev. 1.0, 02/03, page 578 of 1294