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CHAPTER 14 SERIAL INTERFACE 20
14.1 Serial Interface 20 Functions
Serial interface 20 has the following three modes.
Operation stop mode
Asynchronous serial interface (UART) mode
3-wire serial I/O mode
(1)
Operation stop mode
This mode is used when serial transfer is not performed. Power consumption is minimized in this mode.
(2)
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.
It is recommended that the ceramic/crystal oscillation be used for the system clock in UART mode.
If the internal clock is selected as the source clock of the baud rate generator, the transmit/reception
operation may not be performed correctly because the RC oscillation has a high frequency deviation.
(3)
3-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, 3-wire serial I/O mode requires less processing
time for data transmission than asynchronous serial interface mode.
Because, in 3-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.
3-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.