XR17V258

Documentation

• Datasheet

  • XR17V258 66MHZ PCI BUS OCTAL UART WITH POWER MANAGEMENT SUPPORT

• Application Notes

  • DAN-183, Migrating from the XR17D15X to the XR17V25X
  • DAN-190, Exar UARTs in RS-485 Applications
  • DAN-189, Exar UARTs in GPS Applications
  • AN-204, UART Sleep Mode
  • AN 209 - Windows & Linux API interface code for PCI/PCIe UARTs’ drivers
  • AN-225 - Installing and Testing a PCI/PCIe UART Serial Port Using a Custom MaxLinear Driver in Linux
  • dan112.pdf

• Manuals

  • PCI/PCIe EEPROM Programming Utility User Manual

• Software

  • PCI UART EEPROM Programming Utility

• Product Flyer

  • 66 MHz 32-bit PCI Bus Dual, Quad and Octal UARTs

• Product Brochure

  • Interface Brochure

Application

• Remote Access Servers
• Storage Network Management
• Factory Automation and Process Control
• Instrumentation
• Multi-port RS-232/RS-422/RS-485 Cards
• Point-of-Sale Systems

Download Software Drivers

Packaging

Parts & Purchasing

Quality & Environmental Data

Click on the links above to download the Certificate of Non-Use of Hazardous Substances.

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.

Frequently Asked Questions

What are the differences between the XR17Cxxx, XR17Dxxx and XR17Vxxx families?

The XR17Cxxx, XR17Dxxx, and XR17Vxxx are all UARTs but have the following basic differences:

• PCI UARTs
• XR17Cxxx – 5V supply, up to 33MHz clock input
• XR17Dxxx – 5V or 3.3V supply, up to 33MHz clock input
• XR17V2xx – 3.3V supply, up to 66MHz clock input
• PCIe UARTs
• XR17V3xx – 3.3V supply, up to 125MHz clock input

Is an external EEPROM required for the PCI UARTs?

No, it is not required. If an external EEPROM is not detected, the PCI UARTs will use Exar's default Vendor and Device ID. However, we do recommend that you use an EEPROM with your own Vendor and Device IDs.

Can we use 2 PCI UARTs on an add-in card?

Yes, however, you will need to use a PCI-PCI bridge.

Are there any reference designs available?

The schematics for our evaluation boards are available for download from https://www.exar.com/technical-documentation?doctypeid=34

How can my company get a PCI Vendor ID?

You will need to be a member of PCI-SIG. You can find information for becoming a member at www.pcisig.com.

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. 

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.

How do you install and test a PCIe UART serial port using a custom MaxLInear driver in Linux?

See Application Note AN-225 https://www.exar.com/appnote/an-225.pdf

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

When is a 2K pull-up on the XTAL2 output of the UART recommended?

For external clock frequencies above 24MHz at the XTAL1 input, a 2K pull-up may be necessary to improve the rise times if there are data transmission errors.

When using an external clock for the UART, does the duty cycle of the clock have to be 50-50%?

No, it just has to meet the minimum high and low pulse widths.

Can I use a non-standard clock frequency with the UART and still transmit/receive at standard baud rates?

Yes, if you are using a UART with a fractional baud rate generator. This provides a divisor feature with a granularity of 1/16, allowing for any baud rate to be generated by any clock frequency, standard or non-standard. Click on the parametric search button of the product family page and find the Fractional Baud Rate Generator column which tells which products have this feature.

How can the UART wake-up from sleep mode?

The UART will wake-up from sleep mode by any of the following conditions on any channel:

 

-Sleep mode is disabled

-Interrupt is generated

-Data is written into THR

-There is activity on the RX input pin

-There is activity on the modem input pins

 

If the sleep mode is still enabled and all wake-up conditions have been cleared, it will return to the sleep mode.

 

See AN204, UART Sleep Mode for more information on UART Sleep Mode 

Will I receive an interrupt when the UART wakes up from sleep mode if all interrupts are disabled?

For any UART that has the wake-up indicator interrupt, an interrupt will be generated when the UART wakes up even if no other interrupts are enabled.

 

See AN204, UART Sleep Mode for more information on UART Sleep Mode 

What is the difference between LSR bit-6 and LSR bit-5?

LSR bit-6 is a superset of LSR bit-5. The transmitter consists of a TX FIFO (or THR only when FIFOs are not enabled) and a Transmit Shift Register (TSR). When LSR bit-5 is set, it indicates that the TX FIFO (or THR) is empty, however there may be data in the TSR. When LSR bit-6 is set, it indicates that the transmitter (TX FIFO + TSR) is completely empty.

When a Transmit interrupt is generated (ISR = 0xC2), how do I know if it was generated because the TX FIFO is below the trigger level or if the TX FIFO is empty? (This applies only to UARTs with TX FIFO Trigger Levels.)

You can tell by reading LSR bit-5 or bit-6. If they are '0', then the transmit interrupt was generated by the trigger level. If they are '1', then the transmit interrupt was generated by the TX FIFO becoming empty. For enhanced UARTs, you can just read the FIFO level counters.

What is the difference between a RX Data Ready interrupt and a RX Data Timeout interrupt?

An RX Data Ready interrupt is generated when the number of bytes in the RX FIFO has reached the RX trigger level. An RX Data Timeout interrupt is generated when the RX input has been idle for 4 character + 12 bits time.

Which interrupt has a higher priority? The RX Data Ready interrupt or RX Data Timeout interrupt?

For some UARTs, the RX Data Timeout interrupt has a higher priority and in others, the RX Data Ready interrupt has a higher priority. See the interrupt priority section of the datasheet.

I am not able to transmit or receive data, what could be wrong?

The UART requires a clock and a valid baud rate in order to transmit and receive data. Check that there is a clock signal on the XTAL1 input pin. Also, valid divisors need to be written into the DLL and DLM registers. Most UARTs have random (invalid) values upon power-up.

If a character with an error is received, is an LSR interrupt generated immediately or when the character is ready to be read from the RX FIFO?

For most UARTs, the interrupt is generated when the data is ready to be read from the RX FIFO. The are some UARTs that generate the interrupt when the character with the error is received. There are some UARTs that have a register bit to select whether the LSR interrupt is generated immediately or delayed until it is ready to be read.

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.

What conditions are required for enabling the sleep mode in UARTs?

The UART will enter the sleep mode if the following conditions have been satisfied for all channels:

 

-Sleep Mode is enabled

-No interrupts are pending

-TX and RX FIFOs are empty

-RX input pin is idling HIGH (LOW in IR mode)

-Valid values in DLL and DLM registers

-Modem input pins are idle (MSR bits 3-0=0x0)

 

See AN204, UART Sleep Mode for more information on UART Sleep Mode

How can I tell if the UART is in the sleep mode?

There will be no activity on the XTAL2 output.

 

See AN204, UART Sleep Mode for more information on UART Sleep Mode 

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.

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.

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.

What is the advantage of using the UART's 2-character software flow control?

Since 2-character software flow control requires that 2 consecutive flow control characters match before data transmission is stopped or resumes, there is less of a chance that data transmission is stopped because one data byte matched a control character.

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.

In some UARTs, there are 2 sets of FIFO counters. One set is located at the Scratchpad Register location and the other is accessible when LCR = 0xBF. Which one should I use?

It is recommended that the FIFO counters at the Scratchpad Register location be used. When transmitting or receiving data, writing to the LCR register could result in transmit and/or receive data errors.

What is the recommended way for reading the FIFO Counters in the UART?

Due to the dynamic nature of the FIFO counters, it is recommended that the FIFO counter registers be read until consecutive reads return the same value.

In Auto RS485 Half-Duplex control, how does enabling the RS485 mode change the behavior of the interrupt?

In the normal mode, the TX interrupt is generated when the TX FIFO is empty, and there may still be data in the Transmit Shift Register. In the RS485 mode, the TX interrupt is generated when the TX FIFO and the TSR register are both empty.

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.

In auto RS485 Half-Duplex Control, which PCI 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 XR17C158, XR17D152/154/158 and XR17V258 can use the DTR# output as the Auto RS485 control output.

What should be programmed on to the external EEPROM?

The EEPROM needs to have the PCI Vendor ID and Device ID, Subvendor ID and Subsystem Device ID. For more details, see DAN112 https://www.exar.com/appnote/dan112v100.pdf.

Can registers be read or written to in sleep mode?

Yes. Note: some devices do have powersave mode. If UART goes into powersave mode, then the registers are not accessible.

 

See more on Sleep Mode in AN204 UART Sleep Mode.

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.

After the UART wakes up, it can't transmit and receive data. What should be checked?

 

• Check whether the register set can be accessed.
• Check whether the crystal is oscillating fully.
• Check whether the data can be transmitted in internal loopback mode.

 

 

See more on Sleep Mode in AN204 UART Sleep Mode.

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

After enabling sleep mode, the UART isn't going to sleep. Why?

Please check that all the following conditions are satisfied first.

 

• no interrupts pending (ISR bit-0 = 1)
• modem inputs are not toggling (MSR bits 0-3 = 0)
• RX input pin is idling HIGH • divisor (the value in DLL register) is non-zero
• TX and RX FIFOs are empty

 

Be sure sleep mode bit has been set to 1. If there are multiple UART channels, the sleep conditions must be true for all channels.

 

See more on Sleep Mode in AN204 UART Sleep Mode.

Writing a byte of data to the UART doesn't wake it from sleep mode. Why?

Read LSR register to check whether the UART receives the data or not.

 

• If LSR value is 0x60, it means that either UART receiver FIFO doesn’t receive the data or the data in receiver FIFO has been read out before the read of LSR.
• If LSR value is 0x00, it means data is still in the THR (clock doesn’t oscillate to transmit data).
• If LSR value is 0xFF, it means either UART is in powersave mode or UART is powered off. For those devices with powersave mode, be sure that UARTS are not in powersave mode.

 

 

See more on Sleep Mode in AN204 UART Sleep Mode.

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