Datasheet

Table Of Contents
Section 13 Serial Communication Interface
REJ09B0140-0900 Rev. 9.00 Page 423 of 846
Sep 16, 2010
H8S/2215 Group
13.4 Operation in Asynchronous Mode
Figure 13.6 shows the general format for asynchronous serial communication. One frame consists
of a start bit (low level), followed by data (in LSB-first order), a parity bit (high or low level), 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. When the
transmission line goes to the space state (low level), the SCI recognizes a start bit and starts serial
communication. Inside the SCI, the transmitter and receiver are independent units, enabling full-
duplex. Both the transmitter and the receiver also have a double-buffered structure, so data can be
read from or written during transmission or reception, enabling continuous data transfer.
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 13.6 Data Format in Asynchronous Communication
(Example with 8-Bit Data, Parity, Two Stop Bits)