HD64F2357F20V Datasheet, PDF (519/1049 Pages) Renesas Technology Corp – Hardware Manual Renesas 16-Bit Single-chip Microcomputer H8S Family / H8S/2300 Series

14.3.2 Operation in Asynchronous Mode
In asynchronous mode, characters are sent or received, each preceded by a start bit indicating the start of communication
and one or two stop bits indicating the end of communication. Serial communication is thus carried out with
synchronization established on a character-by-character basis.
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.
Figure 14-2 shows the general format for asynchronous serial communication.
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.
One serial communication character consists of a start bit (low level), followed by data (in LSB-first order), a parity bit
(high or low level), and finally one or two stop bits (high level).
In asynchronous mode, the SCI performs synchronization at the falling edge of the start bit in reception. The SCI samples
the data on the 8th pulse of a clock with a frequency of 16 times the length of one bit, so that the transfer data is latched at
the center of each bit.
Idle state
(mark state)
1
LSB
MSB
1
Serial _{0 D0 D1 D2 D3 D4 D5 D6 D7 0/1 1}
1
data
Start
bit
Transmit/receive data
Parity Stop bit
bit
1 bit
7 or 8 bits
1 bit, 1 or
or none 2 bits
One unit of transfer data (character or frame)
Figure 14-2 Data Format in Asynchronous Communication
(Example with 8-Bit Data, Parity, Two Stop Bits)
Data Transfer Format: Table 14-10 shows the data transfer formats that can be used in asynchronous mode. Any of 12
transfer formats can be selected according to the SMR setting.
Rev.6.00 Oct.28.2004 page 489 of 1016
REJ09B0138-0600H