XR21B1411

Documentation

• Datasheet

  • XR21B1411 Enhanced 1-ch Full-Speed USB UART

• Application Notes

  • AN202, USB UART Board Design Considerations for USB Compliance
  • AN205, Comparison of the XR21V1410 and the XR21B1411
  • AN213, USB Basics for the Exar Family of USB UARTS
  • AN217, Enumerating the XR21B1411 USB UART by Location in Windows

• Product Flyer

  • Enhanced 1-CH Full-Speed USB UART
  • Full-Speed USB UART Family

• Chip Shot

  • Chip Image

• Software

  • Sample USB UART GUI
  • Android Application

• Evaluation Board Schematics, Design Files & User’s Manual

  • XR21B1411-0A-EB

• Product Brochure

  • Interface Brochure

Application

• Portable Appliances
• External Converters (Dongles)
• Battery-Operated Devices
• Cellular Data Devices
• Factory Automation and Process Controls
• Industrial Applications

Download Software Drivers

Packaging

Parts & Purchasing

Quality Documents

Frequently Asked Questions

How do I get a driver for my UART?

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.

 

 

You can also get to this link by going to the exar.com website, clicking on Support (in black bar near top of page), then click on Design Tools, then under Evaluation Hardware and Software (towards right of page) click on Software Drivers.

 

 

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. 

Do I need to enable both the UART's Auto RTS and Auto CTS?

No, Auto RTS and Auto CTS are independent. Auto RTS is toggled by the UART receiver. Auto CTS is monitored by the UART Transmitter.

Do I need to enable the UART's Auto RTS and Auto CTS interrupts for Auto RTS and Auto CTS to function properly?

No, Auto RTS and Auto CTS will work normally without the interrupts enabled.

Are software flow control characters loaded into the RX FIFO of the UART?

No, software flow control characters are not loaded into the RX FIFO.

Can I use Auto RTS flow control when Auto RS485 Half-Duplex Control is used?

Auto RS485 Half-Duplex Control feature overrides the Auto RTS flow control feature if both features use the RTS# output pin. Both features can only be used simultaneously if the Auto RS485 control output is not the RTS# output. For some UARTs, the Auto RS485 control output is not the RTS# output.

In Auto RS485 Half-Duplex control, what is the polarity of the RS485 control output?

The polarity of the RS485 control output varies from one UART to another. For some UARTs, an inverter may be required. Some of the newer UARTs have register bits that can change that polarity of the RS485 control output.

What is the maximum data rate supported by the IR Mode in the UART?

All of the UARTs that have the IR mode supports up to 115.2Kbps as specified in IrDA 1.0. The newer I2C/SPI UARTs can support up to 1.152Mbps as specified in IrDA 1.1.

How can I obtain an evaluation board?

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.

What does the -F suffix on the part number mean?

The -F suffix indicates ROHS / Green compliance:
https://www.exar.com/quality-assurance-and-reliability/lead-free-program

How can I find out if the status of a part number is EOL / obsolete or active?

The best way to determine this is to go to maxlinear.com and type the part into the search function. At or near the top of the results you should see something that looks like:

 

 

 

In this example, we looked for XRA1201. Click on part number header or on the link at the bottom of the result.  This brings you to the product page. For example:

 

 

 

Click on Parts & Purchasing, highlighted with the blue arrow above. The screen changes to:

 

 

 

Notice the status column and the “Show obsolete parts” link.  A legend tells you the definition of the different statuses. Click on the “Show obsolete parts” link to see EOL or OBS part numbers along with the Active part numbers, the legend still present:

 

 

 

Another method to find out if a part is OBS or EOL is to click on SUPPORT at the top:

 

 

 

And then Product Change Notifications:

 

  

 

Type the part into the search, and click on one of the part numbers from the drop down menu. Then you can look for the Product Discontinuation Notice, which generally is at the top of the list, for example:

 

 

 

If you see this, it tells you that this particular orderable part has been discontinued and when the last order date is, or was. If you click on the file, then you can view the notice we sent about this if you purchased the part in the recent past. It may also advise of a replacement part. When an orderable part first becomes discontinued, Product Discontinuation Notices are sent are sent to those who have purchased the parts in the recent past, if purchased directly, with a dated opportunity to place a last order.

Should any components be used when connecting a USB host or hub to the USB data pins of MxL USB UARTs, hubs or USB to Ethernet devices?

Connect the USB data pins directly to the host or upstream hub. Connections should be impedance controlled to 90 ohms differential with short traces and no stubs. Connecting any other components that are not high impedance (series or shunt resistance, capacitance or inductance) will corrupt the USB data signaling and can prevent communication between the host and device. ESD protection diodes may be used and some EMI filters may also have only a slight impact on impedance but should be demonstrated for compliance with USB 2.0 devices. See Application Notes AN202 (USB UART Board Design Recommendations and Considerations for USB Compliance), section 2.0 Design Considerations  for more. 

What are the different categories of drivers?

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.

Can I get an example GUI for USB UARTs?

Yes: Go to the product page (XR22804 example below), click on the documentation tab on left, click on “Sample USB UART GUI” under Software:

 

What is the maximum deviation that the UART can tolerate without receiving errors?

It depends on the baud rate. For example, for a start bit, 8 data bits, no stop bit and 1 stop bit, the maximum baud rate deviation is 4.76%. For more information, see https://www.exar.com/appnote/dan108.pdf

In auto RS485 Half-Duplex Control, which USB UARTs can use some other outputs besides RTS# as the RS485 control output?

Most UARTs use RTS#, however in addition to using the RTS# output as the Auto RS485 control output, the XR21B1420/1421/1422/1424 can use the DTR# output as the Auto RS485 control output.

How do I enable RS-485 mode in the MaxLinear custom Linux driver?

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:

 

Change from:

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);

 

For active low TX, change to:

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);

 

For active high TX, change to:

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);

Can the MaxLinear / Exar USB to serial chips work with the standard CDC-ACM driver or do they require the custom driver?

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”.

In older Ubuntu kernels, for example 3.10, how can I use the custom MxL driver for USB UARTs and still use the native CDC-ACM driver for other CDC class devices?

1.  Enter root privileges: sudo -i

2.  Enter admin password.

3.  Edit /etc/modules file.  Append xr_usb_serial_common to the end of the file.

4.  Build the Exar/MxL driver from the folder using "make", confirm that the xr_usb_serial_common.ko file is successfully created.

5.  Run command: uname -r

This will return the kernal version currently in use. 

6.  Copy the resulting xr_usb_serial_common.ko to /lib/modules/2.6.38.8-generic in the above path with the kernal version that was returned in step 5.

7.  Run depmod.

8.  Reboot. 

9.  Connect the Exar/MxL USB UART.  Using ls/dev/tty* confirm /dev/ttyUSBn ports (Exar driver loaded) for Exar/MxL USB UART.

10. Connect another CDC device (not Exar/MxL), and confirm both /dev/ttyUSBn and /dev/ACMn ports. 

How is the USB bus-powered suspend current calculated?

The maximum allowed bus-powered suspend current is 2.5mA per device function. The device function may not be the same as the IC, as there may be multiple device functions per IC. See the individual datasheet for a list of device functions. For example, the XR22804 has 8 device functions: an embedded hub, the Ethernet MAC and Phy, 4 UARTs, I2C controller and EDGE controller. Therefore, the XR22804 maximum allowed bus-powered suspend current is 8 x 2.5mA or 20mA. However, power used by all supporting XR22804 external components that use power from the USB host VBUS power must be included in the suspend current.

Is an inrush limiting circuit needed?

It is recommended, especially when connecting a USB cable to the VBUS 5V source.  See Application Note AN202 (USB UART Board Design Recommendations and Considerations for USB Compliance), section 2.2.2 In-rush Current for more.

When should the OTP be programmed?

The OTP can be programmed to modify various USB configuration descriptors such as Vendor ID, Product ID, Device Attributes and maximum power consumption. See Application Note AN202 (USB UART board Design Considerations for USB Compliance), section 2.3 External EEPROM or on-chip OTP for more. The OTP can also be programmed to change default register values, which can be found in the individual datasheets.

Can we use USB UARTs in audio / video applications?

Once enumeration is completed, the host and device may carry out data transfers. Four type of data transfers are defined: control, bulk data transfers, interrupts and Isochronous data transfers. Although USB UARTs do support the control, bulk data transfers and interrupts, they do not support Isochronous data transfers which would be needed for applications streaming audio or video. See Application Note AN213 (section 3.3.2) for a description of each.