|Information||Enhanced 1-Ch Full-Speed USB UART|
|Data Bus Interface||USB 2.0|
|Max Data Rate 5V (Mbps)||12|
|Max Data Rate 3.3V (Mbps)||12|
|Tx FIFO (Bytes)||512|
|Rx FIFO (Bytes)||512|
|Auto Flow Control||✔|
|Multidrop (9-bit) Mode||✔|
|Fractional Baud Rate Generator||✔|
|Power Down Mode||✔|
|Supply Voltage Range VCC (V)||3.0 to 3.6, 4.4 to 5.25|
|5V Tolerant Inputs||✔|
|Max UART/GPIO Input Voltage (V)||5.5|
|Max UART/GPIO Output Voltage (V)||3.6|
|Temperature Range (°C)||-40 to 85|
|Auto Half-Duplex Control||✔|
|# of Channels||1|
The XR21B1420 is an enhanced Universal Asynchronous Receiver and Transmitter (UART) bridge to USB interface. The USB interface is fully compliant to the USB 2.0 (Full-Speed) specification with 12 Mbps USB data transfer rate. The USB interface also supports USB suspend, resume and remote wakeup operations. The USB Vendor ID, Product ID, power mode, remote wakeup support, maximum power, and numerous other settings may be programmed in the on-chip OTP memory via the USB interface.
The XR21B1420 includes an internal oscillator and does not require an external crystal/oscillator. Any UART baud rate up to 12 Mbps may be generated with this internal clock and the fractional baud rate generator. The UART pins may also be configured as GPIO; direction, state, output driver type and input pull-up or pull-down resistors are programmed either through on chip OTP, or on the fly via memory mapped registers.
Large 512-byte TX and RX FIFOs prevent buffer overflow errors and optimize data throughput. Automatic half-duplex direction control and optional multi drop (9-bit) mode simplify both hardware and software in half-duplex RS-485 applications.
The XR21B1420 uses the native OS CDC-ACM driver or an MaxLinear supplied custom driver. MaxLinear provides WHQL/HCK-certified software drivers for Windows 2000, XP, Vista, 7, 8, 8.1 as well as software drivers for Windows CE, Linux and Mac OS X. Full source code is available.
The XR21B1420 operates from a single 5V or 3.3V power supply. When powered with 5V input, a regulated 3.3V output is supplied.
- ±15kV ESD on USBD+/USBD-
- USB 2.0 Compliant, Full-Speed (12Mbps)
- Unique pre-programmed USB serial number
- Internally generated 48MHz core clock
- Enhanced UART features
- Baud rates up to 12 Mbps
- Fractional Baud Rate Generator
- 512-byte TX and 512-byte RX FIFOs
- Auto Hardware / Software Flow Control
- Multidrop and Half-Duplex Modes
- Auto RS-485 Half-Duplex Control
- Selectable GPIO or Modem I/O
- Up to 10 GPIOs
- 5V tolerant GPIO inputs
- Suspend state GPIO configuration
- Configurable clock output
- 28-pin QFN package
- Industrial -40°C to +85°C Temperature Range
- Download Software Drivers
- Building Automation
- Security Systems
- Factory and Process Control
- ATM Terminals
- USB to Serial Controllers
Documentation & Design Tools
|Data Sheets||XR21B1420 Enhanced 1-Ch Full-Speed USB UART||2D||September 2022||930.6 KB|
|Application Notes||DAN-190, MaxLinear UARTs in RS-485 Applications||2||December 2022||2.3 MB|
|Application Notes||AN202, USB UART Board Design Considerations for USB Compliance||June 2021||647.5 KB|
|Application Notes||AN-226, Windows Driver Customization for USB UARTs||R00||February 2020||2.5 MB|
|User Guides & Manuals||XR21B14xx_XR21V14xx USB UART Design Guide||01||May 2020||2.3 MB|
|User Guides & Manuals||XR21B1420 Evaluation Board User’s Manual||1B||January 2020||1.2 MB|
|Software: GUIs & Utilities||Sample USB UART GUI (Serial Test App)||22.214.171.124||July 2021||1.4 MB|
|Software: GUIs & Utilities||Android Application||1C||November 2015||476.6 KB|
|Product Flyers||Full-Speed USB UART Family||1.1||November 2020||605.3 KB|
|Software: Drivers||Linux 3.6.x and Newer||1D||September 2021||29.9 KB|
|Software: Drivers||Windows XP, Vista, 7, 8, 8.1, 10||126.96.36.199||December 2019||145.7 KB|
|Software: Drivers||XRUSB1 for Win XP SP3 and newer||188.8.131.52||March 2016||1 MB|
|Software: Drivers||Linux 2.6.18 to 3.4.x||1A||January 2015||19.1 KB|
|Schematics & Design Files||XR21B1420/1421 Evaluation Board Design Files||REV 10||June 2016||386.5 KB|
|Schematics & Design Files||Evaluation Board Schematic||1.0||September 2014||88.9 KB|
|Product Brochures||Interface Brochure||October 2022||3.8 MB|
Quality & RoHS
|Part Number||RoHS | Exempt||RoHS||Halogen Free||REACH||TSCA||MSL Rating / Peak Reflow||Package|
Click on the links above to download the Certificate of Non-Use of Hazardous Substances.
Parts & Purchasing
|Part Number||Pkg Code||Min Temp||Max Temp||Status||Buy Now||Order Samples|
Active - the part is released for sale, standard product.
EOL (End of Life) - the part is no longer being manufactured, there may or may not be inventory still in stock.
CF (Contact Factory) - the part is still active but customers should check with the factory for availability. Longer lead-times may apply.
PRE (Pre-introduction) - the part has not been introduced or the part number is an early version available for sample only.
OBS (Obsolete) - the part is no longer being manufactured and may not be ordered.
NRND (Not Recommended for New Designs) - the part is not recommended for new designs.
FAQs & Support
Search our list of FAQs for answers to common technical questions.
For material content, environmental, quality and reliability questions review the Quality tab or visit our Quality page.
For ordering information and general customer service visit our Contact Us page.
Submit a Technical Support Question As a New Question
For some UARTs, Microsoft certified drivers are available for Windows Operating System and can be downloaded via Windows Update. These drivers and others, including for Linux and other Operating Systems can be found by visiting https://www.exar.com/design-tools/software-drivers Please note Software Driver Use Terms.
Click on the version link under Driver Version of the desired type of UART, part number and operating system. A zip file is downloaded which contains a ReadMe file with instructions.Links to datasheets and product family pages are in the software driver table for easy reference.
Find the product page of the part that you want to get an evaluation board for and click on Parts & Purchasing. Example:
Find the icons under Buy Now or Order Samples:
Click on the Buy Now icon and see who has stock and click on the Buy button:
Alternatively, you can click on the Order Samples
If the icons are missing, then contact Customer Support.
The Parts & Purchasing section of the product page shows the Status of all orderable part numbers for that product. Click Show obsolete parts, to see all EOL or OBS products.
USB peripheral devices may operate in bus or self-powered modes. In bus powered mode, the peripheral device is powered by the USB host 5V VBUS power either directly, or for example through a voltage regulator that might provide a regulated 3.3V to the device from the 5V VBUS input. In self-powered mode, power to the peripheral device comes from another source other than the USB host VBUS. For example, power might come from an AC to DC converter.
MaxLinear USB to serial / UART(s), USB hubs and USB to Ethernet devices all comply fully to USB standards and are fully USB compliance tested. One USB compliance test ensures that self-powered peripheral devices do not have “back voltage” when disconnected from the USB host, on either the USB data signals (USBD+ / USBD-) or the VBUS power itself.
All MaxLinear USB UARTs, hubs and USB to Ethernet devices are USB full speed or high-speed devices. As such, they have an internal pull-up on the USBD+ signal to “advertise” their speed rating. The VBUS_SENSE pin on these devices must be connected to VBUS from the host, or upstream device if that is not the host, such that the device “senses” the disconnection from the host or upstream device. The default power mode advertised to the USB host for all USB UARTs and USB to Ethernet devices is bus powered mode. Self-powered mode can be programmed in either the internal OTP memory or external EEPROM for self-powered mode. For MaxLinear hubs, an external pin controls the power mode advertised to the USB host, except the XR22417 which must always be operated in self-powered USB mode.
1. Native drivers: Native drivers may be found in all major OS such as Windows, Linux, and Max OSX. Typically these drivers will be automatically loaded. In some cases, these are basic drivers and may have limitations on advanced device functionality, however. USB HID, Hub and CDC-ACM drivers are examples of native drivers. The CDC-ACM driver be used with our CDC-ACM class USB UARTs, but has limited functionality.
2. MaxLinear custom drivers: MaxLinear custom drivers may be used to support additional functionality in MaxLinear devices. For example, the MaxLinear custom driver for USB UARTs overcomes the limitations of the native CDC-ACM driver. See https://www.exar.com/design-tools/software-drivers for a list of and access to the drivers that we currently have. In some cases, the MaxLinear driver can also be customized, or source code can be provided after executing a Software License Agreement.
Yes: Go to the product page (XR22804 example below), click on the documentation tab on left, click on “Sample USB UART GUI” under Software:
The following lines of code must be modified in the xr_usb_serial_hal.c file in the xr_usb_serial_set_flow_mode function at the end of the function:
xr_usb_serial_set_reg(xr_usb_serial, xr_usb_serial->reg_map.uart_flow_addr, flow);
xr_usb_serial_set_reg(xr_usb_serial, xr_usb_serial->reg_map.uart_gpio_mode_addr, gpio_mode);
xr_usb_serial_set_reg(xr_usb_serial, xr_usb_serial->reg_map.uart_flow_addr, 0x0);
xr_usb_serial_set_reg(xr_usb_serial, xr_usb_serial->reg_map.uart_gpio_mode_addr, 0x3);
xr_usb_serial_set_reg(xr_usb_serial, xr_usb_serial->reg_map.uart_flow_addr, 0x0);
xr_usb_serial_set_reg(xr_usb_serial, xr_usb_serial->reg_map.uart_gpio_mode_addr, 0xB);
All of MaxLinear / Exar's USB UARTs are CDC class / CDC-ACM compliant, except for XR21B1421 which is an HID class device. This means they can use a native CDC driver. All major OS have native CDC drivers, except Windows prior to Windows 10.
None of the MaxLinear / Exar USB UARTs require their custom driver, however they will have certain limitations when not using it. The native CDC driver is not capable of accessing the internal memory map of any device. As a result, when using the native CDC driver, the device “defaults” to a particular configuration. The main implications of this default configuration are that hardware RTS/CTS flow control is enabled and that other settings / advance settings are not configurable. Some devices, for example the XR21B1411 which has an internal OTP memory, can be programmed to change this default configuration, but the configuration cannot be changed “on the fly”.