Operation In Asynchronous Mode; Data Transfer Format - Hitachi H8S/2378, H8S/2378R Series Hardware Manual

15.4

Operation in Asynchronous Mode

Figure 15.2 shows the general format for asynchronous serial communication. One frame consists
of a start bit (low level), followed by transfer 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. In asynchronous serial communication, the
communication line is usually held in the mark state (high level). The SCI monitors the
communication 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.
1 LSB
Serial
0 D0
data
Start
bit
1 bit
Figure 15.2 Data Format in Asynchronous Communication
15.4.1

Data Transfer Format

Table 15.10 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. For details on the multiprocessor
bit, refer to section 15.5, Multiprocessor Communication Function.
Rev. 1.0, 09/01, page 658 of 904
D1 D2 D3 D4
Transmit/receive data
7 or 8 bits
One unit of transfer data (character or frame)
(Example with 8-Bit Data, Parity, Two Stop Bits)
MSB
D5 D6 D7 0/1
Parity
bit
1 bit,
or none
Idle state
(mark state)
1
1 1
Stop bit(s)
1 or
2 bits