Datasheet

Section 16 Serial Communication Interface (SCI, IrDA)
(The H8S/2695 is not equipped with an IrDA function)
R01UH0166EJ0600 Rev. 6.00 Page 759 of 1434
Mar 02, 2011
H8S/2633 Group, H8S/2633 F-ZTAT
TM
,
H8S/2633R F-ZTAT
TM
, H8S/2695
16.3.2 Operation in Asynchronous Mode
In asynchronous mode, characters are sent or received, each preceded by a start bit indicating the
start of communication and 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 16.2 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 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.
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 16.2 Data Format in Asynchronous Communication
(Example with 8-Bit Data, Parity, Two Stop Bits)