Universal synchronous asynchronous receiver transmitter (USART) RM0033
630/1381 RM0033 Rev 9
24 Universal synchronous asynchronous receiver
transmitter (USART)
This section applies to the whole STM32F20x and STM32F21x family, unless otherwise
specified.
24.1 USART introduction
The universal synchronous asynchronous receiver transmitter (USART) offers a flexible
means of full-duplex data exchange with external equipment requiring an industry standard
NRZ asynchronous serial data format. The USART offers a very wide range of baud rates
using a fractional baud rate generator.
It supports synchronous one-way communication and half-duplex single wire
communication. It also supports the LIN (local interconnection network), Smartcard Protocol
and IrDA (infrared data association) SIR ENDEC specifications, and modem operations
(CTS/RTS). It allows multiprocessor communication.
High speed data communication is possible by using the DMA for multibuffer configuration.
24.2 USART main features
• Full duplex, asynchronous communications
• NRZ standard format (Mark/Space)
• Configurable oversampling method by 16 or by 8 to give flexibility between speed and
clock tolerance
• Fractional baud rate generator systems
– Common programmable transmit and receive baud rate of up to 7.5 Mbit/s when
the APB frequency is 60 MHz and oversampling is by 8
• Programmable data word length (8 or 9 bits)
• Configurable stop bits - support for 1 or 2 stop bits
• LIN Master Synchronous Break send capability and LIN slave break detection
capability
– 13-bit break generation and 10/11 bit break detection when USART is hardware
configured for LIN
• Transmitter clock output for synchronous transmission
• IrDA SIR encoder decoder
– Support for 3/16 bit duration for normal mode
• Smartcard emulation capability
– The Smartcard interface supports the asynchronous protocol Smartcards as
defined in the ISO 7816-3 standards
– 0.5, 1.5 stop bits for Smartcard operation
• Single-wire half-duplex communication
• Configurable multibuffer communication using DMA (direct memory access)
– Buffering of received/transmitted bytes in reserved SRAM using centralized DMA
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