
Rev. 2.0, 11/00, page 468 of 1037
23.3.2
Operation in Asynchronous Mode
In asynchronous mode, characters are sent or received, each preceded by a start bit indicating the
start of communication and followed by 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 SCI1, 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 23.2 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 SCI1 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 SCI1 performs synchronization at the falling edge of the start bit in
reception. The SCI1 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(s)
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 23.2 Data Format in Asynchronous Communication
(Example with 8-Bit Data, Parity, Two Stop Bits)
Содержание Hitachi H8S/2191
Страница 123: ...Rev 2 0 11 00 page 96 of 1037...
Страница 149: ...Rev 2 0 11 00 page 122 of 1037...
Страница 197: ...Rev 2 0 11 00 page 170 of 1037...
Страница 247: ...Rev 2 0 11 00 page 220 of 1037...
Страница 249: ...Rev 2 0 11 00 page 222 of 1037...
Страница 347: ...Rev 2 0 11 00 page 320 of 1037...
Страница 357: ...Rev 2 0 11 00 page 330 of 1037...
Страница 417: ...Rev 2 0 11 00 page 390 of 1037...
Страница 431: ...Rev 2 0 11 00 page 404 of 1037...
Страница 439: ...Rev 2 0 11 00 page 412 of 1037...
Страница 457: ...Rev 2 0 11 00 page 430 of 1037...
Страница 525: ...Rev 2 0 11 00 page 498 of 1037...
Страница 543: ...Rev 2 0 11 00 page 516 of 1037...
Страница 639: ...Rev 2 0 11 00 page 612 of 1037 28 1 2 Block Diagram Figure 28 1 shows a block diagram of the servo circuits...
Страница 845: ...Rev 2 0 11 00 page 818 of 1037...