Renesas SH7781 用户手册

21.   Serial Communication Interface with FIFO (SCIF) 

Rev.1.00  Jan. 10, 2008  Page 1074 of 1658 
REJ09B0261-0100 

 

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 64-stage FIFO buffer structure, so that 
data can be read or written during transmission or reception, enabling continuous data 
transmission and reception. 

Figure 21.7 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 
with frequency of 16 times the bit rate. 

LSB

Start

bit

MSB

Idle state

(mark state)

Idle state

(mark state)

Stop bit

0

Transmit/receive data

D0

D1

D2

D3

D4

D5

D6

D7

0/1

1

1

1

1

Serial
data

Parity

bit

1 bit

1 or 2 bits

7 or 8 bits

1 bit or 
none 

One unit of transfer data (character or frame)