
200
User’s Manual U15017EJ2V0UD
CHAPTER 13 ASYNCHRONOUS SERIAL INTERFACE
13.1 Functions of Asynchronous Serial Interface
The asynchronous serial interface (UART) offers the following two modes.
Operation stop mode
Asynchronous serial interface (UART) mode (with pin switching function)
(1) Operation stop mode
This mode is used when serial transfer is not performed to reduce the power consumption.
In operation stop mode, P25/R
X
D0/SI0, P26/T
X
D0/SO0, and P27/ASCK0/SCK0 can be used as a general-purpose
input port or 3-wire serial interface 0 (SIO0).
(2) Asynchronous serial interface (UART) mode (with pin switching function)
This mode is used to send and receive 1-byte data that follows the start bit, and supports full-duplex transmission.
A UART-dedicated baud rate generator is provided on-chip, enabling transmission at any baud rate within a broad
range.
The baud rate can also be defined by dividing the input clock to the ASCK0 pin.
The asynchronous serial interface (UART) and 3-wire serial interface 0 (SIO0) cannot be used at the same time
because they share pins.
These modes can be switched by setting asynchronous serial interface mode register 0 (ASIM0) and serial
operation mode register 0 (CSIM0) (refer to
Table 13-1
).
Table 13-1. Switching Asynchronous Serial Interface Mode and 3-Wire Serial I/O Mode
ASIM0
CSIM0
Operation Mode Selection
Bit 7 (TXE0)
Bit 6 (RXE0)
Bit 7 (CSIE0)
0
0
0
Operation stop mode
0
0
1
3-wire serial I/O 0 (SIO0) mode
0
1
0
Asynchronous serial interface (UART) mode
1
0
0
1
1
0
Other than above
Setting prohibited
Caution
Pins that are not switched can be used as port pins.