SN8F5708 datasheet(134/204 Pages) SONIX

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SN8F5708 Series

UART

Datasheet Rev. 2.4

134

20 UART

The UART provides a flexible full-duplex synchronous/asynchronous receiver/transmitter. The serial

interface provides an up to 0.25MHz flexible full-duplex transmission. It can operate in four modes

(one synchronous and three asynchronous). Mode0 is a shift register mode and operates as

synchronous transmitter/receiver. In Mode1-Mode3 the UART operates as asynchronous

transmitter/receiver with 8-bit or 9-bit data. The transfer format has start bit, 8-bit/ 9-bit data and

stop bit. Transmission is started by writing to the S0BUF register. After reception, input data are

available after completion of the reception in the S0BUF register. TB80/RB80 bit can be used as the

9th bit for transmission and reception in 9-bit UART mode. Programmable baud rate supports

different speed peripheral devices.

The UART features include the following:



Full-duplex, 2-wire synchronous/asynchronous data transfer.



Programmable baud rate.



8-bit shift register: operates as synchronous transmitter/receiver



8-bit / 9-bit UART: operates as asynchronous transmitter/receiver with 8 or 9-bit data bits and

programmable baud rate.

20.1

UART Operation

The UART UTX and URX pins are shared with GPIO. In synchronous mode, the UTX/URX shared pins

must set output high by software. In asynchronous mode (8-bit/9-bit UART), the UTX shared pins

must set output high and URX set input high by software. Thus, URX/UTX pins will transfers to

UART purpose. When UART disables, the UART pins returns to GPIO last status.

The UTX/URX pins also support open-drain structure. The open-drain option is controlled by PnOC

bit. When PnOC=0, disable UTX/URX open-drain structure. When PnOC=1, enable UTX/URX

open-drain structure. If enable open-drain structure, UTX/URX pin must set high level (IO mode

control will be ignored) and need external pull-up resistor.

The UART supports interrupt function. ES0 is UART0 transfer interrupt function control bit. UART

transmitter and receiver interrupt function is controlled by ES0. When ES0 = 0, disable

transmitter/receiver interrupt function. When ES0 = 1, enable UART transmitter/ receiver interrupt

function. UART transmitter and receiver interrupt function are share interrupt vector 0x0023.

When UART interrupt function enable, the program counter points to interrupt vector to do UART

interrupt service routine after UART operating. TI0/RI0 is UART0 interrupt request flag, and also to

be the UART operating status indicator when interrupt is disabled. TI0 and RI0 must clear by

software.

UART provides four operating mode (one synchronous and three asynchronous) controlled by

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