原标题：Exar XR21B1411 USB UART解决方案

　　Exar公司的XR21B1411是增强性能带USB接口的通用异步接收和发送器(UART),其USB接口和全速USB 2.0标准兼容,支持12Mbps USB数据传输速率,内部时钟可编程成6, 12, 24 或 48 MHz,因此不需要外接晶体/振荡器. 128字节TX FIFO,384字节RX FIFO以及7, 8或 9 数据位,主要用在手持设备,外接转换器,以电池为能源设备,蜂窝数据设备, 工厂自动化和过程控制以及工业应用.本文介绍了XR21B1411主要特性,方框图以及XR21B1411评估板电路图.

　　XR21B1411 ENHANCED 1-CH FULL-SPEED USB UART

　　The XR21B1411 (B1411) is an enhanced Universal Asynchronous Receiver and Transmitter (UART) with a USB interface. The USB interface is fully compliant to Full Speed USB 2.0 specification that supports 12 Mbps USB data transfer rate. The USB interface also supports USB suspend, resume and remote wakeup operations.

　　The B1411 operates from an internal clock that is programmable to 6, 12, 24 or 48 MHz. Therefore, no external crystal / oscillator is required as in previous generation UARTs. With the fractional baud rate generator, any baud rate up to 12 Mbps can be accurately generated using the internal clock.

　　The large 128-byte Tx FIFO and 384-byte Rx FIFO of the B1411 help to optimize the overall data throughput for various applications. The Automatic Transceiver Direction control feature simplifies both the hardware and software for half-duplex RS-485 applications. If required, the multidrop (9-bit) mode with automatic half-duplex transceiver control feature further simplifies typical multidrop RS-485 applications.

　　The Vendor ID, Product ID, bus-powered mode, self-powered mode, Remote Wakeup support or Maximum Power Consumption values, as well as default baud rate settings can be programmed using the on-board OTP through the USBD+ / USBD- pins.

　　The B1411 operates from a single 5V power supply and is available in a 16-pin QFN package.

　　WHQL certified software drivers for Windows 2000, XP, Vista, 7, and CE, as well as Linux and Mac are supported for the XR21B1411.

　　XR21B1411主要特性:

　　•±15kV HBM ESD on USBD+/USBD-

　　•USB 2.0 Compliant, Full-Speed (12 Mbps)

　　■Supports USB suspend, resume and remote wakeup operations

　　•Enhanced UART Features

　　■Data rates up to 12 Mbps

　　■Fractional Baud Rate Generator

　　■128 byte TX FIFO

　　■384 byte RX FIFO

　　■7, 8 or 9 data bits

　　■1 or 2 stop bits

　　■Odd, even, mark, space or no parity

　　■Automatic Hardware (RTS/CTS or DTR/DSR) Flow Control

　　■Automatic Software (Xon/Xoff) Flow Control

　　■Multidrop mode

　　■Auto Transceiver Control

　　■Half-Duplex mode

　　■Selectable GPIO or Modem I/O

　　•Internal 48 MHz clock with clock divisors programmable down to 6 MHz

　　•Single 5V power supply

　　•16-pin QFN package

　　•Virtual COM Port WHQL certified drivers

　　■Windows 2000, XP and Vista, 7

　　■Windows CE 4.2, 5.0, 6.0

　　■Linux

　　■Mac

　　XR21B1411应用:

　　•Portable Appliances

　　•External Converters (dongles)

　　•Battery-Operated Devices

　　•Cellular Data Devices

　　•Factory Automation and Process Controls

　　•Industrial applications

　　图1.XR21B1411 方框图