Renesas H8S/2158, User Manual

Page: 471 / 929

Section 16 Serial Communication Interface (SCI, IrDA, and CRC)
Rev. 3.00 Jan 25, 2006 page 417 of 872
REJ09B0286-0300
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.
LSB
Start
bit
MSB
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)
Figure 16.3 Data Format in Asynchronous Communication
(Example with 8-Bit Data, Parity, Two Stop Bits)