Operation In Asynchronous Mode; Figure 12.2 Data Format In Asynchronous Communication (Example With 8-Bit Data, Parity, Two Stop Bits) - Renesas H8SX/1500 Series Hardware Manual

12.4

Operation in Asynchronous Mode

Figure 12.2 shows the general format for asynchronous serial communication. One frame consists
of a start bit (low level), followed by transmit/receive data, a parity bit, and finally stop bits (high
level). 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. 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 transmission and reception.
1
Serial
0
data
Start
bit
1 bit
Figure 12.2 Data Format in Asynchronous Communication
LSB
D0 D1 D2 D3
Transmit/receive data
7 or 8 bits
One unit of transfer data (character or frame)
(Example with 8-Bit Data, Parity, Two Stop Bits)
Section 12 Serial Communication Interface (SCI)
MSB
D4 D5 D6 D7
Parity
bit
1 bit or
none
Rev. 3.00 Mar. 14, 2006 Page 405 of 804
Idle state
(mark state)
1
0/1 1 1
Stop bit
1 or 2 bits
REJ09B0104-0300