User manual

...the world's most energy friendly microcontrollers
2012-04-24 - Giant Gecko Family - d0053_Rev0.96 446
www.energymicro.com
17 USART - Universal Synchronous Asynchronous
Receiver/Transmitter
0
1 2 3 4
USART
RX/
MISO
TX/
MOSI
DMA
controller
RAM
CLK
CS
EFM32
SPI
USART
SmartCards
IrDA
Quick Facts
What?
The USART handles high-speed UART, SPI-
bus, SmartCards, and IrDA communication.
Why?
Serial communication is frequently used in
embedded systems and the USART allows
efficient communication with a wide range of
external devices.
How?
The USART has a wide selection of operating
modes, frame formats and baud rates. The
multi-processor mode allows the USART
to remain idle when not addressed. Triple
buffering and DMA support makes high data-
rates possible with minimal CPU intervention
and it is possible to transmit and receive large
frames while the MCU remains in EM1.
17.1 Introduction
The Universal Synchronous Asynchronous serial Receiver and Transmitter (USART) is a very flexible
serial I/O module. It supports full duplex asynchronous UART communication as well as RS-485, SPI,
MicroWire and 3-wire. It can also interface with ISO7816 SmartCards, and IrDA devices.
17.2 Features
• Asynchronous and synchronous (SPI) communication
• Full duplex and half duplex
• Separate TX/RX enable
• Separate receive / transmit 2-level buffers, with additional separate shift registers
• Programmable baud rate, generated as an fractional division from the peripheral clock
(HFPERCLK
USARTn
)
• Max bit-rate
• SPI master mode, peripheral clock rate/2
• SPI slave mode, peripheral clock rate/8
• UART mode, peripheral clock rate/16, 8, 6, or 4
• Asynchronous mode supports
• Majority vote baud-reception
• False start-bit detection
• Break generation/detection
• Multi-processor mode
• Synchronous mode supports
• All 4 SPI clock polarity/phase configurations
• Master and slave mode
• Data can be transmitted LSB first or MSB first