Operation In Asynchronous Mode; Figure 16.3 Data Format In Asynchronous Communication (Example With 8-Bit Data, Parity, Two Stop Bits) - Renesas H8S/2158 User Manual

16.4

Operation in Asynchronous Mode

Figure 16.3 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 transmission line is usually held in the mark
state (high level). The SCI monitors the transmission 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 transfer and reception.
1
Serial
0
data
Start
bit
1 bit
Figure 16.3 Data Format in Asynchronous Communication
Section 16 Serial Communication Interface (SCI, IrDA, and CRC)
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)
MSB
D4 D5 D6 D7 0/1
Parity
bit
1 bit or
none
Rev. 3.00 Jan 25, 2006 page 417 of 872
Idle state
(mark state)
1
1 1
Stop bit
1 or 2 bits
REJ09B0286-0300