RM0312 datasheet(226/275 Pages) STMICROELECTRONICS

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Universal synchronous/asynchronous receiver transmitter (USART)

RM0312

226/275

DocID022352 Rev 3

21.3

USART functional description

The interface is externally connected to another device by three pins (see Figure 81). Any

USART bidirectional communication requires a minimum of two pins: USART Receive data

input (USART_RX) and USART transmit data output (USART_TX):

USART_RX is the serial data input. Over-sampling techniques are used for data recovery

by discriminating between valid incoming data and noise.

USART_TX is the serial data output. When the transmitter is disabled, the output pin returns

to its I/O port configuration. When the transmitter is enabled and nothing is to be

transmitted, the pin is at high level.

Through these pins, serial data is transmitted and received in normal USART mode as

frames including:

•

An Idle Line prior to transmission or reception

•

A start bit

•

A data word (8 or 9 bits) least significant bit first

•

1 and 2 STOP bits indicating that the frame is complete

•

A status register (USART_SR)

•

Data register (USART_DR)

•

16-bit baud rate prescaler (USART_BRR)

Refer to the register description for the definitions of each bit.

The following pin is required to interface in synchronous mode:

USART_CK: Transmitter clock output. This pin outputs the transmitter data clock for

synchronous transmission (no clock pulses on start bit and STOP bit, and a software

option to send a clock pulse on the last data bit). This can be used to control

peripherals that have shift registers (e.g. LCD drivers). The clock phase and polarity

are software programmable.

RM0312 датащи(PDF) 226 Page - STMicroelectronics