R01UH0823EJ0100 Rev.1.00
Page 1018 of 1823
Jul 31, 2019
RX23W Group
33. Serial Communications Interface (SCIg, SCIh)
33.3
Operation in Asynchronous Mode
shows the general format for asynchronous serial communications.
One frame consists of a start bit (low level), transmit/receive data, a parity bit, and stop bits (high level).
In asynchronous serial communications, the communications line is usually held in the mark state (high level).
The SCI monitors the communications line. When the SCI detects a low, it regards that as a start bit and starts serial
communication.
Inside the SCI, the transmitter and receiver are independent units, enabling full-duplex communications. 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 transmission and reception.
Figure 33.5
Data Format in Asynchronous Serial Communications
(Example with 8-Bit Data, Parity, 2 Stop Bits)
33.3.1
Serial Data Transfer Format
lists the serial data transfer formats that can be used in asynchronous mode.
Any of 18 transfer formats can be selected according to the SMR and SCMR setting. For details of multi-processor
function, refer to
section 33.4, Multi-Processor Communications Function
.
0
Transmit/receive data
D0
0/1
1
Idle state
(mark state)
LSB
MSB
D1
D2
D3
D4
D5
D6
D7
1
Parity bit
1 or 0 bit
Stop bit
1 or 2 bits
7 or 8 bits
One unit of transfer data (character or frame)
Start bit
1 bit
Serial data