RX610 Group
20. Serial Communications Interface (SCI)
R01UH0032EJ0120 Rev.1.20
Page 641 of 1006
Feb 20, 2013
20.3
Operation in Asynchronous Mode
Figure 20.4 shows the general format for asynchronous serial communications.
One frame consists of a start bit (low level), transmit/receive data, a parity bit, and stop bits (high level).
In asynchronous serial communications, the communications line is usually held in the mark state (high level).
The SCI monitors the communications line, and when it goes to the space state (low level), recognizes a start bit and
starts serial communications.
Inside the SCI, the transmitter and receiver are independent units, enabling full-duplex communications. 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 transmission and reception.
0
Transmit/receive data
D0
0/1
1
1
1
Idle state
(mark state)
LSB
MSB
D1
D2
D3
D4
D5
D6
D7
1
Parity bit
1 or 0 bit
Stop bit
1 or 2 bits
7 or 8 bits
One unit of transfer data (character or frame)
Start bit
1 bit
Serial data
Figure 20.4 Data Format in Asynchronous Serial Communications
(Example with 8-Bit Data, Parity, Two Stop Bits)