![](http://datasheet.mmic.net.cn/380000/-PD789187_datasheet_16744969/-PD789187_63.png)
Preliminary Product Information
63
μ
PD789186, 789187, 789196, 789197
6.8
Serial Interface
6.8.1
Serial interface 20
(1) Functions of serial interface 20
Serial interface 20 has the following three modes.
Operation stopped mode
Asynchronous serial interface (UART) mode
Three-wire serial I/O mode
(a) Operation stopped mode
This mode is used when serial transfer is not performed. Power consumption is minimized in this mode.
(b) Asynchronous serial interface (UART) mode
This mode is used to send and receive the one byte of data that follows a start bit. It supports full-duplex
communication.
Serial interface 20 contains a dedicated UART baud rate generator, enabling communication over a wide
range of baud rates. It is also possible to define baud rates by dividing the frequency of the input clock
pulse at the ASCK20 pin.
(c) Three-wire serial I/O mode (switchable between MSB-first and LSB-first transmission)
This mode is used to transmit 8-bit data, using three lines: a serial clock (SCK20) line and two serial data
lines (SI20 and SO20).
As it supports simultaneous transmission and reception, three-wire serial I/O mode requires less
processing time for data transmission than asynchronous serial interface mode.
Because, in three-wire serial I/O mode, it is possible to select whether 8-bit data transmission begins with
the MSB or LSB, serial interface 20 can be connected to any device regardless of whether that device is
designed for MSB-first or LSB-first transmission.
Three-wire serial I/O mode is useful for connecting peripheral I/O circuits and display controllers having
conventional clock synchronous serial interfaces, such as those of the 75X/XL, 78K, and 17K series
devices.
(2) Serial interface 20 configuration
Serial interface 20 consists of the following hardware.
Table 6-12. Serial Interface 20 Configuration
Item
Configuration
Register
Transmission shift register (TXS20)
Reception shift register (RXS20)
Reception buffer register (RXB20)
Control register
Serial operation mode register 20 (CSIM20)
Asynchronous serial interface mode register (ASIM20)
Asynchronous serial interface status register (ASIS20)
Baud rate generator control register (BRGC20)