HT85F2270 datasheet(200/226 Pages) HOLTEK

200 / 226 page

Rev. 1.00

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Standard 8051 8-Bit Flash MCU

HT85F2260/HT85F2270/HT85F2280

UART0 Operating Description

This section provides a more detailed description of the UART0 structure and operation. The

following shows the overall UART0 block diagram.

UART0 Baud Rate

Transmit Shift Register

Control Unit

Output

Latch

RXD0

RI0

TI0

Receive Shift Register

Input

Latch

S0BUF

RXD0

TXD0

�CU Data Bus

UART 0 Block Diagram

UART0 External Pin Interfacing

To communicate with an external serial interface, the UART0 has two external pins known as

TXD0 and RXD0. The UART0 provides four operating modes which can be categorised into

two transmitter/receiver methods, so called Synchronous and Asynchronous. In Synchronous

communication, the MCU must be the master device and the TXD0 pin is used to provide the

shift clock while the RXD0 pin is used as the data transmitter/receiver pin. In Asynchronous

communication, which does require a clock signal, the TXD0 pin is used to transmit data while the

RXD0 pin is used as the data receive pin. The TXD0 and RXD0 pins are pin shared with I/O pins.

When the UART0 function is disabled, controlled by the REN0 bit in the S0CON register, these

two pins can be used as general purpose I/O pins.

HT85F2270 Datasheet(PDF) 200 Page - Holtek Semiconductor Inc